WebGL - How to pass unsigned byte vertex attribute colour values?

Question

My vertices are made up of an array with this structure:

[     Position      ][        colour        ]
[float][float][float][byte][byte][byte][byte]

Passing the vertex position is no problem:

gl.bindBuffer(gl.ARRAY_BUFFER, this.vbo);
gl.vertexAttribPointer(this.material.aVertexPosition, 3, gl.FLOAT, false, 4, 0);

But I can't figure out how I can pass the colours to the shader. Unfortunately, it's not possible to use integers inside the glsl shader so I have to use floats. How can I get my unsigned byte colour value into the glsl float colour value? I tried it like this for r, g and b sepperately but the colours are all messed up:

gl.bindBuffer(gl.ARRAY_BUFFER, this.vbo);
gl.vertexAttribPointer(this.material.aR, 1, gl.BYTE, false, 15, 12);

Vertex Shader (colouredPoint.vs)

precision highp float;

attribute vec3 aVertexPosition;
attribute float aR;
attribute float aG;
attribute float aB;

uniform mat4 world;
uniform mat4 view;
uniform mat4 proj;

varying vec3 vVertexColour;

void main(void){
    gl_PointSize = 4.0;  
    gl_Position = proj * view * world * vec4(aVertexPosition, 1.0);
    vVertexColour = vec3(aR, aG, aB);
} 

Pixel Shader (colouredPoint.fs)

precision highp float;

varying vec3 vVertexColour;

void main(void){
    gl_FragColor = vec4(vVertexColour, 1);
} 

Solution 1

gl.vertexAttribPointer(this.material.aVertexPosition, 3, gl.FLOAT, false, 4, 0);
gl.vertexAttribPointer(this.material.aR, 1, gl.BYTE, false, 15, 12);

Your stride should be 16, not 15 and certainly not 4.

Also, each individual color does not need to be a separate attribute. The four bytes can be a vec4 input. Oh, and your colors should be normalized, unsigned bytes. That is, the values on the range [0, 255] should be scaled to [0, 1] when the shader gets them. Therefore, what you want is:

gl.vertexAttribPointer(this.material.aVertexPosition, 3, gl.FLOAT, false, 16, 0);
gl.vertexAttribPointer(this.material.color, 4, gl.UNSIGNED_BYTE, true, 16, 12);

Oh, and attributes are not materials. You shouldn't call them that.

Solution 2

GLfloat red=(GLfloat)red/255;

I hope that's what you are looking for ^^

Comments

[Markus]

Thanks, but I tried that already. It just darkens the points. gebackene-ente.at/nudelsalat/sonstiges/webgl_01.png gebackene-ente.at/nudelsalat/sonstiges/webgl_02.png

[Markus]

Thank you. I missunderstood the stride to be the gap between one set of data to the next. I tried to normalize colours before but what I was missing was the UNSIGNED_BYTE type. Material is an object that contains the shader, its attributes and some material settings so I think its just right to call it material. Works now.

[Whiskas]

That's weird because I'm using this in C++ and it works pretty well, are you sure that your float have enough precision ?

[Markus]

See Nicol Bolas answer for the solution. I was passing gl.BYTE instead of gl.UNISGNED_BYTE and I've got the stride wrong.