Level Design for Dawn of War tutorial

Level Design for Dawn of War

Welcome, here is a set of tutorials dealing with the Mission Editor for Dawn of War. These tutorials will enable you to understand each stage in the creation of a fully functioning skirmish map.

Contents and Overview:
Newbies Guide to Alpha Channels and Layers
First steps in the Mission Editor
Concepts you will need to know, and the absolute basics of the Mission Editor.

HeightMaps in the Mission Editor
HeightMaps in Photoshop
How terrain geometry is made, inside and outside of the Mission Editor.

Colouring and detailing terrain
Texture Stamping
Detail Textures
Decals
The layers terrain is made from; how each works and how they interact.

Texture file format comparison
Finishing touches and useful links
Information you will need to know in order to confidently make custom textures, and how to finish your map.

Newbies Guide to Alpha Channels and Layers:

You will need to know about these in order to make custom maps for Dawn of War.

Alpha maps:

Alpha maps are 2D greyscale images. Here are some examples:

They are used for two purposes in Dawn of War:

• Heightmaps
• Transparencies

Here is an example of the checker pattern alpha map being used to define the height of a terrain sheet in the editor:

The basic, flat terrain sheet of a new map generated in the Mission Editor.

The checker pattern distorts the terrain sheet, defining high and low areas.

(Dont worry about being able to do this for now, it will be explained later).

Here is an example of alpha maps being used to define transparency:

On the left is a standard Relic decal depicting a crater, with the standard Relic alpha channel dictating which parts are transparent. At the top is the decal graphic with no transparency, and on the right is the same decal graphic using the checkerboard pattern from the alpha channels shown above.

Because alpha channels are made from black, white and 254 shades of grey, they allow you to define 256 different levels of height when making an alpha channel for terrain, and 256 levels of transparency when making alpha channels for texture art. As you can see above, the Relic crater decal blends smoothly with the background because it uses shades of grey.

Don't worry if you don't understand what decals or heightmaps are, that will be explained in a later part of these tutorials.

In terms of alpha transparency: White is opaque, black is transparent, and all shades of grey depict varying translucency. In terms of terrain height, white is highest and black is lowest.

Layers:

Layers are an important concept in mapping for DoW, because the terrain is made from several of them. Anyone with experience of Adobe Photoshop will probably find it very easy to understand how they work in the Dawn of War mission editor.

For those unfamiliar with them, think of a single image made from several sheets of glass placed on top of each other; each sheet bearing a single part of the image, which in turn occludes some of the image on the sheets below. By way of a quick example, in the image above that shows craters, the crater decals are on one layer, and the blurry pattern that surrounds them is another layer which sits below. This separation means that you can manipulate the different layers of terrain quite independently of each other, the only real dependency being that all of them will conform to the alpha channel that dictates the shape of the terrain.

First Steps:

If you are not already familiar with alpha channels and layers, refer to a guide covering the basics.

How Dawn of War Terrain Works:

The terrain in Dawn of War is made from several specific layers. From the lowest to the highest, these are:

• Heightmap: This defines the terrain geometry.
• Texture Stamping: This provides the rough colour information for the whole terrain.
• Detail textures: Provide patterned detailing, and some further colour information.
• Decals: Provide fine details that can be unique, and placed precisely.

The exact functions and technicalities of each of these layers will be explored in later tutorials.

The Mission Editor:

The Dawn of War Mission Editor (ME) is focused on painting rather than geometry, which might be a difficult adjustment if you've come to it from a background of 3D art or first-person-shooter design tools. If however you have any background with painting, digital or otherwise, it might be easier.

Firstly, you will need the mod tools for Dawn of War, as they do not ship with the game. They are available in a slim exe and vital files only package (11Mb) or a full version with included art samples (75Mb). You can download them from MODDB.

New Map:

Ready to begin? Right then. Load the ME (Located here: [game_folder]\W40kME.exe) and hit new. The mission editor will present you with a dialogue box, from which you can select the size of your map and whether it is for a mod or the normal game.

A general rule for map sizes is to use 256*256 for 1v1 maps, and 512*512 for anything bigger. 1024*1024 is unstable. If you need a clearer idea of map sizes, they are shown in game when you are selecting from the skirmish maps:

Leave the default Cell Size at 2m. This defines the grid that placed object models will snap to by default.

Next you must select from the mod list: Use "WarHammer 40,000 Dawn of War" for skirmish maps.

Once you've done this, the editor will present you with a basic terrain sheet.

Viewing the Map:

With the default viewing options, you will not be able to see much of your map at once. This is because the fog and the sky model are cutting off the outer extents of the terrain sheet. Hit CTRL+K and CTRL+F, which respectively toggle the fog and the sky.

Other important keyboard shortcuts for looking at the map are the arrow keys, with which you scroll around the map, backspace, which sets the camera to the default angle and range, like in game, and alt+mouse, which changes the camera angle, as it does in game with "Full 3D Camera" enabled in the game options.

Only the central section of the terrain sheet is avaliable for gameplay, the border is reserved for detail to give an appearance of surrounding landscape when the camera is rotated in game. You can see the approximate proportion of usuable terrain in this shot of Deadman's Crossing. The rectangle deliniated in red is the play area of the map:

To see the play area on any map, go to the Overlay menu, and experiement with different combinations of the avalable options. On a new map, Terrain Type shows the play area most obviously, but later, when you have terrain built up around the edge of the map, ImpassEdit Map gives a clearer picture. Any such overlays can be turned off with the Toggle Overlay command at the top of the Overlay menu.

Scenario and Terrain Properties:

On the file menu, under "Scenario", you will find the Scenario Properties. From here you can define the map name: convention is the map title, followed by the number of players in brackets. This is the text that will show up in the map selection list.

Below that you can set map type: Skirmish/Multiplayer Map or Single Player Mission. None in this set of tutorials will deal specifically with single player missions, though you will need the same general editing skills as for skirmish maps.

The last area is for the map description, which will also show up in the map selection screen.

Below Scenario Properties on the Scenario menu, you will find Terrain Properties. From here you can choose Sunight Colour, Shadow Colour, and Time of Day (In the first public release of the mod tools, placing the time of day slider close to Morning, Noon or Night could create lighting bugs, and it was advised elsewhere that it be placed between those times. However, in version 1.10 of the tools, buggy time of day settings are locked out).

Below that you can choose a sky and scale it; change the camera angle to see it, and toggle the fog with CTRL+F if you want to see it more clearly.

Experiment with fog start distance, end distance, and colour to get what you want.

Detail texture repeat allows you to scale detail textures, which are covered in a later tutorial.

Under the Water heading, there isn't much to choose from, but you can change the colour of the water along with certain other properties such as scaling and animation speed. Water is explained in the tutorial on heightmaps.

You can also toggle sky, water and terrain rendering from these options; for now it is recommended that you leave them on.

Map Naming and File Structure:

When you save a map, the correct file naming convention is [playercount]_[mapname].sgb

So for instance, "2p_deadmans_crossing.sgb" or "4p_biffys_peril.sgb". When you save a file, it must be saved in [game_directory]\W40k\Data\Scenarios\, with skirmish maps in the MP folder and single player in SP.

When a map is saved, 4 files are created. These are your .sgb file, which contains the map itself, and three .tga image files. Basically, one of these holds colour information for the terrain, and the other two are the icon and minimap that show up in the map selection screen and the HUD. For now these don't matter, we will return to them later.

ME UI and Toolbar:

Here is an image of the ME:

At the top, as with any application, you can see the menu bar and the toolbar. On the right is a tray which gives you information and options relating to whatever tool you have selected. The main black area is the 3D viewport in which you will be looking at your map.

Note: the tray is slightly buggy; often when you are using tools and change a setting in the tray, it will keep hold of the focus of your mouse pointer and as a result it will seem as if the 3D viewport has become unresponsive. To fix this when it occurs, just left click on a blank area of the tray, then start working in the 3D viewport again.

Here is an image of the most important buttons on the toolbar:

They are:

1. Select Objects
2. Object Placement
3. Decal Placement
4. Markers
5. Heightmap Editor
6. Texture Stamping
7. Detail Map Editor
8. Terrain Type Editor
9. Impass Map Editor

Each function will be explained in detail later, with the exception of markers, which are not particularly relevant to skirmish maps.

Object Placement:

When this is selected from the tool bar, the tray on the right of the ME displays a branching list of avaliable objects. In this list you can find all of the decorative objects used in the game, as well as objects vital to gameplay. Gameplay objects are found under "environment > gameplay", and they include slag heaps, critical locations, strategic points, relics, and most importantly starting locations. Once you begin creating a map, you will also want to make sure it is at the right scale, which can be checked by temporarily placing buildings and units.

To place an object, first select it in the list, then left click in the 3D view where you want to place it. Further left clicks will keep on placing objects of the same type.

To move a placed object around, left click on it and hold the mouse button down, then move the mouse (Remember though, this won't work unless you are using the object placement tool).

To delete a placed object, select it then press your delete key. You can select objects individually by left clicking and dragging slightly, then letting go of the button, or you can select a group of objects by clicking away from them, holding the button down, and drag selecting them with a box. Though you can select in this way using the Object Selection and Object Placement tools, deleting can only be done when you switch to the Object Placement tool.

The height of objects will be set automatically by the height of the terrain where you place them, and if you drag them around their height will adjust accordingly. If you try to drag an object onto a piece of terrain that too steep or otherwise impassable, it will spring back to its previous location. You can also adjust height manually on most objects by selecting them, holding down shift, then clicking and dragging with the right mouse button. Notice though that Relics, Slag Heaps, Critical and Strategic Locations all reset themselves to terrain height automatically.

If you need to reset the height of an object, you can snap it to the terrain by clicking the "Relative to Terrain" radio button in the tray, then the "Snap" button next to it.

Objects you place will snap to the default grid setting you selected when you were going through the new map dialogue, but with the settings in the tray you can also define a larger grid setting and specify that your object selection snaps to it.

"Use Random Rotation" causes objects to be oriented at a random 90 degree rotation upon placement. Selected objects can be rotated after placement by moving the mouse while holding down SHIFT+Left Mouse Button, though they will still snap to 90 degree increments.

Finally, the "Player:" drop down list is what is used to define the owners of objects. All gameplay and decorative objects must be set to owner World, if they are not they will not show up in game. The only exceptions are the starting locations, which need to be set up sequentially with the player numbers.

Hey Presto:

You should now be able to make a a working skirmish map on a flat terrain sheet by placing starting locations and requisition points. Not very pretty or exciting to play though, is it? Those are the basics; the next tutorials will deal with the techniques and tools needed to make a proper map.

eightmaps in the Mission Editor:

The Basics:

Select the Heightmap Editor from the ME toolbar. When you move the cursor over the terrain, you should see a pair of white circles drawn beneath it. These are the brush with which you will paint and sculpt the terrain.

The options in the tray are:

• Mode: Additive, Subtractive, Set Value, and Smoothing
• Brush Size: This controls the outer circle of your cursor (Moving the mouse while holding down SHIFT+Left Mouse Button will also change the size of the brush).
• Feather: This controls the size of the inner circle of your brush.
• Height: Allows you to set an explicit value, which only works when "Mode" is set to "Set Value"
• Presets: A usesful set of named, selectable height values.
• Strength: Allows you to adjust the magnitude of your brush.

All the terrain within the inner circle of your cursor will be affected at the strength you set. Between the perimeters of the two circles, the effect fades uniformly from maximum strength to nothing. When using Addition or Subtraction, holding the mouse button down and moving the mouse will generate some extreme results. The best results come from gradually bulding up the terrain, so remember: short, controlled bursts.

Set levels will raise or lower the terrain to the preset height you choose.

Smoothing will get rid of any jaggedness, as shown in the before and after images below:

Water Level:

The level of the water is fixed at a single value which cannot be changed. It runs under the map as a continuous sheet, and to make it show you have to lower the terrain past it; there are relevant preset levels in the terrain editing options. Water sometimes won't show up properly where it should until after the map file is saved.

Terrain Type Editor:

The first option in the tray is a drop down list. "FootFall" is not implementd, so ignore it. The other item on the list is Cover. The game does not automatically make craters into heavy cover, etc, you have to paint it on yourself.

The drop down list is buggy, sometimes the bottom one will show the wrong option, and sometimes they'll hold on to the mouse pointer focus and make the 3D viewport seem unresponsive, so double check them.

The only four options on the cover list you need are None, Light, Heavy, and Negative, which will be self explanatory to anyone who has played the game.

Blocking and Stealth cover are not implemented. Blocking is meant to prevent the construction of buildings, and stealth is meant to automatically cloak any units within it. They don't work though.

Painting Impass Maps:

The impass map tells units what areas they can stand on and travel over, and what areas they cannot. The ME will automatically generate an impass map on the basis of what gradient a piece of terrain has, but as you can see in the picture below, it is not perfect:

You have to use the Impass Map Editor to tweak it. The list in the tray has three options:

• Generated: This resets terrain you paint to the ME generated default impass map.
• Passable: This explicitly denotes terrain as passable, no matter how steep it is. This shows in a brighter shade of grey than the default passable terrain.
• Impassable: This explicitly denotes terrain as impassable, no matter how flat it is. This shows in a brighter shade of red than the default impassable terrain.

Terrain Bugs:

These mainly come in the form of jaggies, which will occur all over your terrain whether it is done in the ME or an external editor. As with the example pictures above, the smoothing tool can sort them out, shown by these images of the bottom of a steep cliff descending into water:

Jaggies will have several effects, including distorted decals and placed meshes being absorbed in part by the terrain or hovering above it. Such effects can be minimised with the smoothing and other terrain tools, though never completely eliminated. The most obvious example would be the terrain above the water on Deadman's Crossing: some of the strategic points hover slightly, and the ground tends to absorb parts of building meshes, which is especially visible with the Machine Cults and Eldar portals.

Jaggies will also create small fragments of impassable terrain, viewable with the Impass Map tool. A quick and dirty cheat to get rid of them is to just paint them as passable with the Impass Map Editor, but a better solution is to use the smoothing tool and if necessary additive and subtractive painting to even out the ground.

Another terrain bug to look out for is paths that are too narrow for vehicles. Or would that just be a feature? ;)

A final, very important thing to note is that working bridges are not possible in Dawn of War. Basically, if units can travel over something, anything underneath will become impassable, so take that into account when you design.

Heightmaps in Photoshop:

Using Photoshop or a similar external editor to edit heightmaps offers some massive benefits over the ME tools.

If you don't know how to use Photoshop, your library should have a selection of books on it, or be able to get some. I recommend SAMS Teach Yourself Photoshop in 24 Hours, as it imparts a solid grounding in most aspects of the program.

First, you'll need to export your heightmap from the ME. Go to File > Export > Heightmap, then choose a location and name for it.

Painting Heightmaps:

Brief recap: White = high, black = low.

monoRAIL has made a rather handy image that correlates grey values with the ME Terrain Tool set levels. It certainly makes it easier to know what you're painting: external link to image

Once you have the heightmap open in Photoshop, you'll need to set the image up to show exactly where the play area is and where the border is. Guides are a good way to do this:

That heightmap measures 256*256 pixels, and the vertical and horizontal guides set at 64 and 192 pixels mark the 128*128 play area in the centre. Having guides also showing the exact centre is useful when you come to select, duplicate and rotate elements of the image, such as the flat topped hills you can see in the central area of the image above.

The ME is very friendly to exporting and importing heightmaps. Simply save it in Photoshop, then in the ME go to "File > Import > Heightmap" and select your file. The import shouldn't take more than a second or two, allowing you to quickly see the effects of your Photoshop work.

Handy Tricks:

Painting very fine gradiations seems almost impossible when the grey values are only a few points apart. However, if your graphics card allows it (and if it can run Dawn of War, it really should ;) ), then set the gamma way up in your graphics options and you'll be able to see exactly what you're doing at lower levels. Here's a shot of part of a coastline from a heightmap, showing it normally first, then with a simulated high gamma value:

Suddenly, very fine differences are highly visible and tunable. How high exactly you need to raise your gamma settings will depend upon your monitor.

Just to be clear: you won't be changing the brightness of the file, you'll be changing the brightness of your display. If you changed the brightness of the alpha map in order to see fine details, it would work in a similar way, but the bits of the map already at higher brightness values would cap out at 255, then be completely flat once you lowered the brightness and reimported the heightmap to the ME.

The blur tool is the equivalent to the ME smoothing tool, though you have to be careful about it bleeding outward and causing slopes to become gentler than you want them to be. Usually I find it better to do most of my editing in Photoshop then import the heightmap and use the ME smoothing tool to get rid of the jaggies.

A huge advantage Photoshop has over the ME tools is that you can mirror your terrain exactly, thus avoiding any players moaning about balance in your maps. Mirroring terrain horizontally or vertically is easy using the selection and transform tools. Mirroring it diagonally is a bit more obtuse, so here's an explanation:

Select the polygonal lasso tool, then, making sure that anti-aliasing and feathering are off, and that it will snap to guides, select two edges of the central play area, then join them diagonally across the middle. Copy and paste the selection into a new layer, then rotate it 90 degrees and perform one flip (Which way you rotate and flip depends on which half you selected).

Voila! It will leave a minor seam down the middle, but it's nothing you can't get rid of with the basic painting, blur and smudge tools.

Finally, the biggest advantage of using Photoshop is that you can save your heightmap as a PSD file, and use it to separate terrain features onto their own layers. This allows you to add, transform, and erase entire landforms without disturbing other parts of your heightmap.

Overview of Terrain Layers:

This section is an overview of the three layers mentioned earlier:

• Texture Stamp
• Detail texture
• Decals

Using Sand Storm from the Community Map Pack II as an example, here are some images showing what the three layers do and how they interact.

Here is a normal shot of the map with all layers showing:

Here, in the first shot, is the texture stamp layer of the map on its own. To show the effect it has on the decals and detail textures, the second shot shows the complete map with a pure pink texture stamp layer:

Here are two comparison images of the detail textures over a pure black texture stamp layer and a pure white one:

Still using the black and white texture stamps, here are closer comparisons of each detail texture used in the map, the first one also interacting with the water sheet:

In order to show the decals clearly, here are two images of the map with no detail textures and a white texture stamp:

This leads us into the next part of this section: Texture Stamping

Texture Stamping:

The texture stamp is like the first stages of a painting. It is the lowest colour layer of your terrain, which basically allows you to paint in rudimentary colour information that will show through the transparencies of any detail textures and decals you place.

Texture stamping cannot be undone in the editor. The only way to get rid of it is to paint over it with something else. Here is the default texture stamp image that is given to a new map:

As you can see, it is a basic pattern designed to give variance of texture and shade to anything placed on top of it.

Select the texture stamping tool from the ME toolbar. you will find a basic description of the options in the tray on this page of the RDN. To quote it:

• Spacing: This modifies that the textures will "space" apart when you are "painting" with a given texture. Painting in this case is defined as clicking and dragging the mouse on the world map. This creates several instances of a given texture.
• Strength: This determines the "strength" of the brush. Think of this as the "opacity" of the current texture. A low strength texture is "see-through," for example.
• Color: This will modify the color of the given texture, but note that the original color of the texture is taken into account, so you will only get the color you picked when the texture itself is pure white, otherwise you will get a combination of your chosen color and the texture color.
• Refresh Base Texture: This will reset the base texture to what it was before any type of paint was applied to it. You will be asked to confirm your choice before this command is executed.

"Refresh Base Texture" will not reset the Texture Stamp map to the default unless that is what was last saved in the current session with the ME. It simply reloads the file it was saved to, which is:

[game_folder]\W40k\Data\Scenarios\MP\[yourmapname].tga

As with a heightmap, you can edit this file using either the relevant tools in the ME or an external painting program. Saving the map will save the TGA file also, though if you change it in an external editor, using the ME reset function will reload your newly saved TGA, allowing you to easily check your work.

Here is a size comparison image of the basic ME brushes:

There are other presets to experiment with.

Warning: All of these brushes are large. BRUSH_SOFT_TINY16 is almost as wide as a Space Marine HQ is long.

Inside the ME, painting can only be started inside the playable area of the map, though you can then drag your brush outside the area to paint the borders. If it behaves erratically, try changing the camera angle.

Unfortunately, I currently have little expertise in painting, so can only give scant advice on how to use texture stamping effectively: Load other custom maps, or use an sga unpacker (such as Spooky Rat's or Corsix') to extract the official maps from [game_folder]\W40k\W40kData.sga, then load them in the ME and pick them apart to see how they have been painted.

Detail textures:

Detail textures are laid on a very large grid. In the ME, select Detail Map Editor from the toolbar. You will see a white grid mesh hovering under your cursor in the 3D viewport, showing where a single instance of a detail texture can be painted by left clicking.

This tool is slightly buggy in the 1.10 tools. Dragging will paint all of the squares you drag the cursor across, but this ony works properly within the playable area of the map. Dragging outside may have unpredictable results, such as whole stripes of terrain being painted at once. This can be minimised by using single clicks to paint rather than dragging. If it behaves erratically within the play area, for instance by ceasing to paint, try changing the camera angle.

Alpha maps:

As mentioned in the previous section, Texture Stamping only shows through the grey and black areas of detail texture and decal alpha maps. Detail textures with no alpha transparency or a white alpha channel will completely cover any texture stamping you have done. Often, this is a source of confusion for people new to the ME: they lay a detail texture down that has no transparency, then try texture stamping and assume it isn't doing anything.

In the images below, you can see four different detail textures and the way they interact with the Texture Stamp:

Custom Detail Textures:

If you want to use your own texture art, it must be saved in DDS or TGA format at base2 resolutions (Typically 128*128, 256*256, and 512*512). An examination of texture formats and resolutions can be found in part 9 of these tutorials.

Any custom detail textures you make should be saved in [game directory]\WH40K\Data\Art\scenarios\textures\detail\

Once they are saved there, the ME will find them upon loading and add them to the tray list of detail textures. If the ME is already open they will not show up as you save them.

Different texture sizes effectively only change the resolution of the painted areas, not the size of the square terrain section that is painted. While appearing more detailed, a higher resolution image will cover the same amount of terrain as a lower resolution version, as shown below by a photograph of a piece of limestone at three different resolutions:

As mentioned in the ME basics section, the tiling of the detail textures can be changed in the Terrain Properties using the Detail Texture Repeat setting, as show below. The first image uses a repeat setting of 1, the second a repeat setting of 2:

The settings will go much higher, but at such levels will tend to scrub out any detail rather than enhance it in any way.

Decals:

Decals sit on top of the Texture Stamp and Detail Textures.

Like objects, decals are selected from a tray list and placed using the left mouse button. They are also rotated by moving the mouse while holding down SHIFT+Left Mouse Button, and similarly they are scaled with SHIFT+Right Mouse Button.

Decals can be moved by clicking the left mouse button and dragging, and can be layed on top of each other. Layer order of decals relative to each other is decided by alphabetical order of the file tree branches. For instance, decals from JUNGLE will sit on top of anything from ALL, but below anything from URBAN. Within each branch of the decal file tree, again, the layer order of decals follows alphabetical order.

So bear that in mind when you're creating custom decals: choose the final directory name before you place them all over and realise you have to redo it because a standard decal you want underneath them is sitting on top!

Custom decals:

Like detail textures, decals must be saved as DDS or TGA at base2 resolutions (Typically 128*128, 256*256, and 512*512).

Any custom decals you make should be saved in this location: [game directory]\WH40K\Data\Art\Decals\[your_folder_name]

Once they are saved there, the ME will find them upon loading and add them to the branching list of decals in the tray. They will not show up as you save them if the ME is already open, you must save them there then load the ME to have it detect them.

The edge pixels of all decal alpha channels must be pure black, i.e. transparent, to prevent odd projections such as these:

Decals can be saved in DDS or TGA image formats. TGA decals will show up in the preview window of the ME tray, DDS will not. Most of the decals that ship with the game are DDS files. As stated in the Detail Textures section, a comparison of texture formats and resolutions can be found in part 9.

If you save your decals as TGA files, they must be saved as 32 bit to have the alpha channel.

Texture Format Comparison:

Information:

• All decals were generated from the same 512 x 512 source art, including the alpha channels.
• All files were made with Photoshop 7, using the file format plugin that allows TGA alpha channels (Info and Download).
• TGAs were saved at 32 bit, as 24 and 16 don't allow alpha maps (More info on that here).
• Map in test shot is 128 x 128.
• Blue and red checker detail texture is DXT1, 256 * 256.

Resolution and Format Comparisons:

Firstly, here is a scale comparison.

Here is a reference shot taken in the Mission Editor, showing all the decals and what formats they are in.

As you can see, the mipmaps of the DDS files are evident in comparison to the TGA decals, especially on the higher resolution decals.

The file sizes of my test decals:

• 512 * 512:
• DXT: 341K
• TGA: 1.0Mb

• 256 * 256:
• DXT: 85.4K
• TGA: 256K

• 128 * 128:
• DXT: 21.4K
• TGA: 64K

DDS files saved with DXT 5 and 3 give identical file sizes.

The major advantage of DDS files is their lower use of VRAM (source), though a few tests seem to indicate that as long as a map is not especially decal intensive, the performance hit caused by using TGAs exclusively is negligible compared to the performance hit caused by the models and effects of the game. DDS decals and textures might enable a map to run on lower spec systems, but the other art assets could soon scupper that :)

Looking through the Relic files, it seems that most decals and detail textures are DXT5 or DXT1 DDS files, with only a few being TGAs.

DDS Alpha Transparency Comparison:

Though DDS files at DXT5 and DXT3 give identical filesizes, DXT alpha maps are clearly stepped, especially on larger decals and detail textures. TGA files and DXT5 DDS files give smooth alphas.

I can't give you empirical answers, but judging by the Relic artwork and a lot of custom content, it seems that 256*256 is the preferable average size for decals and detail textures, with DXT5 being the best way to record transparency. TGAs and 512*512 files seem to be useful for items that are repeated or used rarely and benefit from high detail, such as some of the crater decals.

With thanks to dr2sheds and monoRAIL

Finishing Touches and Useful Links:
Changing Minimaps and Previews:
The other two TGA files generated when you save a map are the icon that show in the map selection screen, and the minimap that shows in the HUD. There are several bugs with these

How to Package Your Map:

While mapping, keep a record of all the custom files you create. With a skirmish map, there are at least the four files created in your Scenarios\MP folder. Additionally, there are the custom icon and minimap TGA files, as well as any custom decals and detail textures. If you have such an array of custom files, reproduce the folder structure away from the Dawn of War Game folder, then copy each of the files required to run your map into the dummy folder structure. Once you've done that, use a program such as Winzip or WinRAR to package the folders up into a single archive file (Some people prefer zip files, though rars offer better compression).

Archiving your map with a folder structure allows anyone who downloads it to simply unzip it into the game directory and play, rather than fiddling with lots of files and a readme that tells them where to put them. If you do that to them instead, they will hate you for it, and rightly so. After all the effort of creating a map, why commit that one act of laziness, eh?

Get some friends to test it to make sure it works, and by "it" I mean both the archive file structure and the map itself. Include a readme text file detailing the map name and map author, along with any relevant websites, contact information, credits and fluff you may wish to put in. Putting this in means that a few years hence, when a player might have a huge heap of custom maps for Dawn of War, they can still find out who made a particular map and possibly track down the rest of the author's work.

Markers:

I pointed these out on the toolbar, but didn't cover them in these tutorials because noone seems to know how relevant they are. Skirmish maps seem to get by fine without them.