How to merge two textures. (noob question).

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jcakec

How to merge two textures. (noob question).

in Programming Questions • 3 years ago

I'm trying to use some GLSL but I have a basic problem.
I have created 4 GLTextures, which I need to render on top of each other:
      1.- render 2 textures
      2.- apply a GLSL filter
      3.- render the other two textures on top of the reulting texture,
      4.- apply another filter.

I tryed using an GLGraphicsOffScreen, but I cannot render a QUAD for rendering the texture, but when I do

gCanvas.beginShape(QUAD_STRIP);
gCanvas.texture(firstTex);
gCanvas.vertex(0, 0 0, 0);
gCanvas.vertex(80, 5, 100, 0);
gCanvas.vertex(95, 90, 100, 100);
gCanvas.vertex(40, 95, 0, 100);
gCanvas.endShape();

I get the error that beginShape(int) is not allowed. Am I missing something?
Is there a way to place a texture on top of another texture? I'm confused on OpenGl and processing OpenGL functions on their objects... maybe a break will help.

thanks in advanced.

Replies(4)

kevin.bjo..

Re: How to merge two textures. (noob question).

3 years ago

Try using GLGraphics GLTexture class and filters to make this straightforward

a sample project: http://www.botzilla.com/blog/archives/000717.html

basically you can just declare targets as GLTextures, then apply GLSL shaders to them as GLFilters

kb, http://www.riftgame.com/

jcakec

Re: How to merge two textures. (noob question).

3 years ago

Thank you kevin,bjorke, I will try this ASAP.

UPDATE: kevin.bjorke, I have read your shaders and those copy the frames, but don't merge them... I am using some alpha on some textures I am creating, so I need a way of merging not copying.

I've used a shader that compares the two pixels (source and dest) and checks if source has alpha the dest pixel is not changed, but does not work exactly as I expected.

kevin.bjo..

Re: How to merge two textures. (noob question).

3 years ago

I'm sorry if you thought I had pre-written your app! I was just showing you a way to apply GLSL shaders to images. You would still need to write the correct GLSL :)

In your case, you want to write a filter with two input textures, which is pretty straightforward.

Here's one from a different program (which I haven't put up on the web yet) that does a simple composite:

First "simpleComp.xml":

<filter name="simpleComp">
    <description>SimpleComposite</description>
    <fragment>simpleComp.glsl</fragment>
    <textures input="2" output="1">
        <intexture type="sampler2d" name="srcSampler" label="source">0</intexture>
        <intexture type="sampler2d" name="pntSampler" label="painted">1</intexture>
    </textures>
</filter>

Next "simpleComp.glsl":

//
// simpleComp.glsl
// 2010 Kevin Bjorke http://www.botzilla.com
// Made for JokerPaint
// Uses Processing & the GLGraphics library
//

uniform sampler2D srcSampler;
uniform sampler2D pntSampler;

void main(void) // fragment
{
    vec4 bkg = texture2D(srcSampler,gl_TexCoord[0].st);
    vec4 pnt = texture2D(pntSampler,gl_TexCoord[0].st);
    vec4 comp;
    comp.rgb = (pnt.rgb)*pnt.a + (bkg.rgb * (1.0-pnt.a));
    comp.a = 1.0;
    gl_FragColor = comp;
}

and in Processing it gets called like so:

simpleComp = new GLTextureFilter(this,"simpleComp.xml");
/** ..... **/
simpleComp.apply(new GLTexture[]{bgTex, accumTex}, destTex);
destTex.render(0,0);

where bbgTex, accumTex, and destTex are all GLTextures

kb, http://www.riftgame.com/

jcakec

Re: How to merge two textures. (noob question).

3 years ago

Thanks kevin.bjorke. I never thought you had prewritten the my app. I was just explaining my problem when using GLSL. I'm at a restaurant right now, but will test the code when I get home. and thank you very much for showing me the correct way of using alpha on GLSL, as I haven't used it there. (always prerendered the frame before passing to GLSL on other apps).

UPDATE: worked great kevin.bjorke, thanks again for your help.

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