Decals in GIMP
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This tutorial describes one process for making a decal in GIMP. GIMP 2.2 was used for these steps and images. Minor details may vary with other versions.
Step 1: Creating a file
Create a new file, with the following settings:
- Width: 1024
- Height: 1024
- Colorspace: RGB Color (under advanced options)
- Fill with: Transparency (under advanced options)
The size can be varied but, since a decal is a material, it must conform to the size requirements for materials. In particular, each dimension must be a power of two.
The size can be smaller (512x512, for example), but better results are often acquired by creating textures at their maximum resolution and later scaling them down as required for their in-game use.
Step 2: Drawing
This step is completely up to you. Good results can be acquired from using various techniques, including:
- custom brushes
- photographic source material
- scanned real-world materials (for example, flicking ink onto blotting paper can produce a good starting point for a blood splatter decal).
Step 3: Collapse all layers
- in the layers palette, right click on any layer and select "Merge Visible Layers..." to merge everything you have to one layer. If keeping the layers is important to you, you will want to save your file before doing this.
Step 4: Opacity
This should select everything you have drawn, by whatever method you can. I like using "select by color", setting the threshold very high, and clicking on a part of the image that I drew.
Now, right click on your layer in the layers palette, and select "Add Layer Mask". In the next dialog, select "Selection", then click OK. You should see the mask show up beside your existing layer in the Layers palette, and also if you open up the Channels palette, you should see the alpha channel there with the appropriate mask. If you want to tweak the pixels in the alpha channel, now is the time to do it; remember that black pixels indicate transparency (none of your pixels you drew will appear) and white pixels indicate opaqueness (the full color of whatever you drew will show).
Step 5: Saving
Before you save, go to the layers palette and click on the drawing part of your layer to deselect the layer mask. Pick also Select|None from the menus.
Go to File|Save As, and type in the filename that you want with a .tga extension. A dialog will pop up telling you that TGA can't handle layer opacity or layer masks; just click Export. On the next dialog, uncheck RLE compression.
That's all! Now you can make a material out of it.
Now proceed to Creating Decals to complete the process.