Question

I have a one big Sprite on the Scene – for example 200×200 and in the app i have an array[200][200] in which i store 0 or 1 for each pixel in big sprite.

I want to draw one more textured sprite (for example 10×10) above existing one, but i want to calculate for eache pixel in new sprite if it needs to draw it on this scene depends on provided array (if in corresponding position of the pixel in new sprite in array is ‘1’ – i need to draw this pixel, if ‘0’ – i don’t want to draw it (maybe set alpha = 0)).

I think i can use fragment shader for each of new sprites, but i can’t understand how to provide array data to the shader to calculate color for each pixel.
I think also can use fragment shader for the whole scene (if render to texture).

I am quite new in opengl and can’t figure out in what way to move.

When i create resources for the scene – i try to create my mask:

    mask = new float[512*512*4];
    for (int i = 0; i < mask.length; i++)
    {
        mask[i] = 2f;
    }

    GLES20.glActiveTexture(GLES20.GL_TEXTURE1);
    GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, 1029384756);
    GLES20.glTexImage2D(GLES20.GL_TEXTURE_2D, 1, GLES20.GL_RGBA, 512, 512, 0, GLES20.GL_RGBA, GLES20.GL_FLOAT, FloatBuffer.wrap(mask));
    GLES20.glTexParameterf(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_MIN_FILTER, GLES20.GL_LINEAR);
    GLES20.glActiveTexture(GLES20.GL_TEXTURE0);

Then when i draw new item on scene i use shader:

    setShaderProgram(ShaderProgram.getInstance());

    GLES20.glActiveTexture(GLES20.GL_TEXTURE1);
    GLES20.glUniform1i(RadialBlurExample.RadialBlurShaderProgram.sUniformMask, GLES20.GL_TEXTURE1);
    GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, 1029384756);
    GLES20.glActiveTexture(GLES20.GL_TEXTURE0);

But i can’t see new item on scene (maskVal is <0.5).

I try to find working way to pass array as a texture but i can’t find it.

Answer 1

Upload your array as a second texture with the same dimensions as the sprite, and then when you draw the sprite, sample the second texture at the same texcoord.

If the second texture doesn’t meet the mask criteria, discard the fragment

uniform sampler2d sprite;
uniform sampler2d mask;
in vec2 uv;
main() {

   float maskVal = texture2D(mask, uv).r;
   if(maskVal > 0.5) {
        gl_FragColor = texture2D(sprite,uv);
   } else {
        discard;
   }
}