Slick Forums

Is there not a built-in way to modulate (multiply) all colors on an image, i.e. color a grayscale image? I wrote one myself just fine; just wondering if I missed anything.

Since we don't have direct access to a texture's pixel data in OpenGL, you need to go about this a little differently. Here's some options...

• Use "vertex colouring" which looks like this in Slick:
  
  Code:
  image.draw(30, 30, Color.red);
  
  Using the above, every color in your image will be multiplied by red (RGB = 1, 0, 0). For example, all white pixels (RGB = 1, 1, 1) will turn red. This is very fast since it's done in hardware, and you can modulate it differently by using texture combiners (OpenGL).
• "Upload" an array of pixel data to the GPU. This is probably what you're doing now, using ImageBuffer (i.e. constructing a texture from an array of pixels). This is relatively slow since (a) ImageBuffer requires creating a new OpenGL texture, (b) ImageBuffer isn't very optimize, (c) you aren't changing the pixel data on the GPU and (d) the upload is not asynchronous (by default) so relying on it heavily may affect performance. For a more efficient and more flexible way of modifying pixel data than ImageBuffer, look into my PixelData utility.
• Fragment shaders. This is generally accepted as the "best" and most efficient manner of modifying images on a per-pixel (or "fragment") basis. This is done in hardware, so it's as fast as vertex colouring. It's generally the way you would do things like invert colours, polar coordinates, advanced blend modes, etc. GLSL is a pretty big topic and it's well outside the scope of Slick, but there are some shader utilities and examples in the dev branch. This site is a really interesting place to learn/dissect GLSL.

Ah, thanks! You were right; I am using ImageBuffer to modulate each color using setRGBA then converting it to an image. But vertex coloring looks like the simplest solution right now; I think I'll go with that. Thanks for the response!