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.

This is GLSL and not HLSL. The type has to be ivec4 for an integral datatype — Rabbid76
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. — derhass

Rhu Mage Rhu Mage · Accepted Answer · 2018-11-06T09:48:58

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.

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

2 Answers