[JAVA3D] TextureUnitStates for terrain rendering

[Hrvoje Smolic]

Hi all!
I was playing with different parameters for texturing my terrain over
weekend, but with no satisfactory results. My idea is to have base layer
(grass), and on top of it replace it with alpha blended different texture
(snow, for example). In that way I will have a nice transition from grass to
snow texture.
 Below are texture attribures for each TextureUnitState. No matter what
parameters I tried, I can't isolate alpha texture to work only on one layer
(snow). Is order of states important? What is best I can get are two
textures combined (which is OK), but than alpha texture cuts off them both,
not only snow (or grass). How could I achieve that?


           //grass
            baseTextAtt = new TextureAttributes();
            baseTextAtt.setTextureMode(TextureAttributes.REPLACE);

            //snow
            mainTextAtt = new TextureAttributes();
            mainTextAtt.setTextureMode(TextureAttributes.COMBINE);
            mainTextAtt.setCombineRgbMode(TextureAttributes.COMBINE_REPLACE);
            mainTextAtt.setCombineRgbSource(0,
TextureAttributes.COMBINE_TEXTURE_COLOR);
            mainTextAtt.setCombineRgbFunction(0,
TextureAttributes.COMBINE_SRC_COLOR);
            mainTextAtt.setCombineAlphaMode(TextureAttributes.COMBINE_MODULATE);
            mainTextAtt.setCombineAlphaSource(0,
TextureAttributes.COMBINE_PREVIOUS_TEXTURE_UNIT_STATE);
            mainTextAtt.setCombineAlphaFunction(0,
TextureAttributes.COMBINE_SRC_ALPHA);

            //alpha mask for snow
            alphaTexAttr = new TextureAttributes();
            alphaTexAttr.setTextureMode(TextureAttributes.COMBINE);
            alphaTexAttr.setCombineRgbMode(TextureAttributes.COMBINE_REPLACE);
            alphaTexAttr.setCombineRgbSource(0,
TextureAttributes.COMBINE_PREVIOUS_TEXTURE_UNIT_STATE);
            alphaTexAttr.setCombineRgbFunction(0,
TextureAttributes.COMBINE_SRC_COLOR);
            alphaTexAttr.setCombineAlphaMode(TextureAttributes.COMBINE_REPLACE);
            alphaTexAttr.setCombineAlphaSource(0,
TextureAttributes.COMBINE_TEXTURE_COLOR);
            alphaTexAttr.setCombineAlphaFunction(0,
TextureAttributes.COMBINE_SRC_ALPHA);

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