Texture Splatting and Lighting

OpenGL Development JOGL Development
#1

Hi, i’ve recently been messing around with texture splatting on a simple landscape demo and am currently blending between two different textures using an alpha map using the following code


		myGL.glActiveTexture(GL.GL_TEXTURE0);
		myGL.glBindTexture(GL.GL_TEXTURE_2D, textures[0]);
				
		myGL.glTexEnvf(GL.GL_TEXTURE_ENV, GL.GL_TEXTURE_ENV_MODE, GL.GL_COMBINE);
		myGL.glTexEnvf(GL.GL_TEXTURE_ENV, GL.GL_COMBINE_RGB, GL.GL_INTERPOLATE);
		
		myGL.glTexEnvf(GL.GL_TEXTURE_ENV, GL.GL_SOURCE0_RGB, GL.GL_TEXTURE0);
		myGL.glTexEnvf(GL.GL_TEXTURE_ENV, GL.GL_OPERAND0_RGB, GL.GL_SRC_COLOR);
		
		myGL.glTexEnvf(GL.GL_TEXTURE_ENV, GL.GL_SOURCE1_RGB, GL.GL_TEXTURE1);
		myGL.glTexEnvf(GL.GL_TEXTURE_ENV, GL.GL_OPERAND1_RGB, GL.GL_SRC_COLOR);
		
		myGL.glTexEnvf(GL.GL_TEXTURE_ENV, GL.GL_SOURCE2_RGB, GL.GL_TEXTURE2);
		myGL.glTexEnvf(GL.GL_TEXTURE_ENV, GL.GL_OPERAND2_RGB, GL.GL_ONE_MINUS_SRC_ALPHA);

Where unit 0 has one texture, unit 1the texture it’s to be blended with and unit 2 contains the alpha map.
Due to the combination, the textures are no longer modulated and as such my lighting is not being displayed. Does anyone know a way for me to retain lighting values whilst blending?

Incidentally, is there any way to get around the constraint of just 4 texture units being available on Nvidia cards for multitexturing use? i have the three units above taken up as well as another unit for the shadowmap. This has left the number of textures on the landscape sadly lacking as i have only a rock/grass transition.

Apologies for the length of the questions and thanks in advance for any help!

#2

Well, I used to first modulate texture0 (ground) with light.
then, bind alpha mask to texture1
finally, interpolate texture2 (grass) with previous two.
that way they will be interpolated, and texture0 (first one) is modulated with light info.

EDIT: As for constraint: Well, here it is and you can’t help it. What you can do is to provide several render methods, for example:
render_with_3_texture_units_available()
render_with_4_texture_units_available()
render_with_5_texture_units_available()
so that you adjust your engine to current configuration.