WebGL 1D texture - shader value catch

Question

So I'm working on computation using GPU shaders in WebGL- In the javascript portion of the code, I put precalculated values onto an array to send as a texture to be read up in the fragment shader-

        var count=0;
        var table = [];
        for (var y = 0.1; y<1; y+=.01) {

            for (var x = 0.1; x<1; x+=.01) {

                var u = x;
                var u2 = y;
                u += u2 * 0.003921568627451;
                u *= 4.0;
                var sig = 1/(Math.exp(2.0 *(u-3)) + 1);

                table.push(Math.floor(sig*255));
                //table.push(255);
                table.push(0);
                table.push(0);
                table.push(0);
                count+=4;


                console.log(Math.floor(sig*255)+"");
                console.log(0+"");
                console.log(0+"");
                console.log(0+"");


            }

        }

        //alert(count);
          //alert(table[101]);

        texturetab = gl.createTexture();

        gl.bindTexture(gl.TEXTURE_2D, texturetab);

        gl.pixelStorei(gl.UNPACK_ALIGNMENT, 1);

        gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, 100, 100, 0,

                      gl.RGBA, gl.UNSIGNED_BYTE, new Uint8Array(table));

        //

        gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.NEAREST);

        gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.NEAREST);

        gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);

        gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);



        gl.uniform1i(gl.getUniformLocation(prog, "uTabSamp"), 2);

but when I "catch" the values of the texture on the shader, the computation acts as if it is only reading values of 0- it's not changing as it should- (Snippet of where the value is caught on the fragment shader) :

        sigmoid =  (texture2D(uTabSamp, vec2(floor(u*100.+.5), floor(u2*100.+.5))).r)/255.;

        float hfunc   = sigmoid * u * u;
        float ffunc   = -u +(a - pow(v*nb,m))*hfunc ;

Seeing as how WebGL is difficult to read, how do I go about fixing this?

david van brink · Accepted Answer · 2013-11-06 21:18:05Z

1

texture2D(uTabSamp, vec2(floor(u*100.+.5), floor(u2*100.+.5))

Texture sample coordinates must range from 0.0 to 1.0. So scale your lookup for the texture size you built.

Your texture-making code isn't shown, but, be sure to set the interpolation to NEAREST (assuming you want exact access to the values), and sample from the "middle" of each pixel. For example, the bottom-left pixel from a 128 x 32 texture will be found at vec2(0.5 / 128.0, 0.5 / 32.0).

answered Nov 6, 2013 at 21:18

david van brink

3,6721 gold badge24 silver badges18 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Skorpius Over a year ago

gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.NEAREST); gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.NEAREST); gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE); gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE); Like so?

Collectives™ on Stack Overflow

WebGL 1D texture - shader value catch

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related