OpenGL GLSL Send color as integer to shader to be decomposed as vec4 RGBA

Question

I can send color to shader as 4 floats - no problem. However I want to send it as integer (or unsigned integer, doesn't really matter, what matters is 32 bits) and be decomposed in vec4 on shader.

I'm using OpenTK as C# wrapper for OpenGL (although it should be pretty much just a direct wrapper).

Let's consider one of the most simple shaders with vertex containing position(xyz) and color(rgba).

Vertex shader:

#version 150 core

in vec3 in_position;
in vec4 in_color;
out vec4 pass_color;
uniform mat4 u_WorldViewProj;

void main()
{
    gl_Position = vec4(in_position, 1.0f) * u_WorldViewProj;
    pass_color = in_color;
}

Fragment shader:

#version 150 core

in vec4 pass_color;
out vec4 out_color;

void main()
{
    out_color = pass_color;
}

Let's create vertex buffer:

public static int CreateVertexBufferColor(int attributeIndex, int[] rawData)
{
    var bufferIndex = GL.GenBuffer();
    GL.BindBuffer(BufferTarget.ArrayBuffer, bufferIndex);
    GL.BufferData(BufferTarget.ArrayBuffer, sizeof(int) * rawData.Length, rawData, BufferUsageHint.StaticDraw);
    GL.VertexAttribIPointer(attributeIndex, 4, VertexAttribIntegerType.UnsignedByte, 0, rawData);
    GL.EnableVertexAttribArray(attributeIndex);
    GL.BindBuffer(BufferTarget.ArrayBuffer, 0);
    return bufferIndex;
}

And I'm getting all zeros for vec4 'in_color' in vertex shader. Not sure what's wrong.

Closest thing what I found: https://www.opengl.org/discussion_boards/showthread.php/198690-I-cannot-send-RGBA-color-as-unsigned-int .

Also in VertexAttribIPointer I'm passing 0 as a stride, because I do have VertexBufferArray and keep data separated. So colors come tightly packed 32 bits (per color) per vertex.

Layla

This is GLSL and not HLSL. The type has to be ivec4 for an integral datatype – Orbicular

I don't think that integer attributes are what you want. You want just UNORM, hence you use in vec4 in conjunction with glVertexAttribPointer. Not glVertexAttribIPointer. – Ruvolo

Answer 1

Aight, so this did the job for me:

Having managed data as int[] where it's tightly packed array of only colors (where int format is: RGBA meaning 0xAABBGGRR), then defining vertex attribute as: GL.VertexAttribPointer(index, 4, VertexAttribPointerType.UnsignedByte, true, sizeof(int), IntPtr.Zero) and using it in shader as: in vec4 in_color;.

Layla

Answer 2

You have to use VertexAttribPointer and not VertexAttribIPointer when the input in your shader are floats (vec4).

Set the normalized parameter to GL_TRUE.

Spec says:

glVertexAttribPointer, if normalized is set to GL_TRUE, it indicates that values stored in an integer format are to be mapped to the range [-1,1] (for signed values) or [0,1] (for unsigned values) when they are accessed and converted to floating point. Otherwise, values will be converted to floats directly without normalization.

Tenancy

It looks logical to do that, however this does not work: GL.VertexAttribPointer(attributeIndex, 4, VertexAttribPointerType.UnsignedByte, true, 0, rawData); (rawData is int[] where integer contains all 32 bits for 4 channels RGBA or ARGB or whichever). I still get vec4 (0,0,0,0) in vertex shader, any ideas? – Layla

If you are trying to pack all 4 channels into a single int, you need to set GL.VertexAttribIPointer(attributeIndex, 1, VertexAttribIntegerType.UnsignedByte, 0, rawData); and in your shader receive just a single uint instead of vec4. Then you can unpack from uint to vec4 with vec4 unpackUnorm4x8(uint p);. Also make sure it's uint and not int. – Tenancy

Aight, so my shader looks like this: #version 400 core in vec3 in_position; in uint in_color; out vec4 pass_color; uniform mat4 u_WorldViewProj; void main() { gl_Position = vec4(in_position, 1.0f) * u_WorldViewProj; pass_color = unpackUnorm4x8(in_color); } and vertex atrributes: GL.VertexAttribIPointer(attributeIndex, 1, VertexAttribIntegerType.UnsignedInt, 0, rawData); You mentioned 'VertexAttribIntegerType.UnsignedByte' where I suppose it should be 'UnsignedInt', however none of them worked anyway, I still get zeros at the shader. – Layla

Yes, should be UnsignedInt. Did you check if rawData actually contains any values? Are you sure attributeIndex is correct? You can try to set it expicitly with: GL.VertexAttribIPointer(1, 1, VertexAttribIntegerType.UnsignedInt, 0, rawData); and in the shader layout(location = 1) in uint in_color;. And is rawData int or uint? Should be uint. – Tenancy

Well I'm still stuck. Simply cannot get it to work. However if I construct only one vertex buffer where I place all attributes in a sequence with stride (instead of building different buffer for attribute), that works just fine: e.g. having position as 3 floats and color as int: GL.VertexAttribPointer(Shader.in_position, 3, VertexAttribPointerType.Float, false, vertexSize, IntPtr.Zero); + GL.VertexAttribPointer(Shader.in_color, 4, VertexAttribPointerType.UnsignedByte, true, vertexSize, new IntPtr(12)); – Layla