Trouble passing attributes to GLSL using LWJGL

Question

I'm trying to learn GLSL and I'm wanting to send a float attribute to my vertex shader. For now, this float is to be used simply to set the brightness (I mulitply in_Color by in_Light and assign it to out_Color). The brightness always seems to equal 1.0 in the vertex shader regardless of what I try to pass (0.1 in the code below). I've tried googling and I've tried experimenting quite a bit but I just don't get what's wrong. Position, texture coordinates and color seem to work fine.

Here is how I'm binding the attribute locations, and a bit more of the code.

    this.vsId = Shader.loadShader(pVertexFilePath, GL20.GL_VERTEX_SHADER);
    this.fsId = Shader.loadShader(pFragmentFilePath, GL20.GL_FRAGMENT_SHADER);

    this.pId = GL20.glCreateProgram();
    GL20.glAttachShader(this.pId, this.vsId);
    GL20.glAttachShader(this.pId, this.fsId);

    GL20.glBindAttribLocation(this.pId, 0, "in_Position");
    GL20.glBindAttribLocation(this.pId, 1, "in_TextureCoord");
    GL20.glBindAttribLocation(this.pId, 2, "in_Color");
    GL20.glBindAttribLocation(this.pId, 3, "in_Light");

    GL20.glLinkProgram(this.pId);

    this.normalMatrixId = GL20.glGetUniformLocation(this.pId, "normalMatrix");
    this.projectionModelViewMatrixId = GL20.glGetUniformLocation(this.pId, "projModelViewMatrix");

This is how I'm setting the position of each attribute

    FloatBuffer verticesFloatBuffer = BufferUtils.createFloatBuffer(verticesCount * 36);
    for (VertexData vert : vertices) {verticesFloatBuffer.put(vert.getElements());}
    vertices.clear();
    verticesFloatBuffer.flip();

    GL30.glBindVertexArray(vaoId);

    GL15.glBindBuffer(GL15.GL_ARRAY_BUFFER, vboId);
    GL15.glBufferData(GL15.GL_ARRAY_BUFFER, verticesFloatBuffer, GL15.GL_STATIC_DRAW);

    GL20.glVertexAttribPointer(0, 3, GL11.GL_FLOAT, false, 36, 0);
    GL20.glVertexAttribPointer(1, 2, GL11.GL_FLOAT, false, 36, 12);
    GL20.glVertexAttribPointer(2, 3, GL11.GL_FLOAT, false, 36, 20);
    GL20.glVertexAttribPointer(3, 1, GL11.GL_FLOAT, false, 36, 32);

    GL15.glBindBuffer(GL15.GL_ARRAY_BUFFER, 0);

This is the getElements method used above (I have manually input color and brightness for testing purposes). Note that the last value which should be in_Light is 0.1f and always turns out to be 1.f in the vertex shader.

public float[] getElements() {
    return new float[]{this.x, this.y, this.z, this.s, this.t, 1.f, 0.f, 1.f, 0.1f};
}

Vertex Shader:

#version 430 core

uniform mat4 projModelViewMatrix;
uniform mat3 normalMatrix;

in vec3 in_Position;
in vec2 in_TextureCoord;
in vec3 in_Color;
in float in_Light;

out vec4 pass_Color;
out vec2 pass_TextureCoord;

void main(void) {
    gl_Position = projModelViewMatrix * vec4(in_Position, 1.0);

    pass_TextureCoord = in_TextureCoord;

    pass_Color = vec4(in_Color * in_Light, 1.0);
}

Fragment Shader (just in case someone wants to see it):

#version 430 core

uniform sampler2D texture_diffuse;

in vec4 pass_Color;
in vec2 pass_TextureCoord;

out vec4 out_Color;

void main(void) {
    out_Color = texture2D(texture_diffuse, pass_TextureCoord) * pass_Color;
}

All other attributes that I pass to the vertex shader work fine.

EDIT: Just as a note, I've tried changing the shader to specify locations, eg:

layout (location = 0) in vec3 in_Position;

I've also used glGetAttributeLocation which gives me the same attribute locations (0, 1, 2, 3), eg:

GL20.glGetAttribLocation(this.pId, "in_Position");

I've also added an if statement to the shader to check the value of in_Light and it always equals one.

EDIT2: Now I've changed the color attribute to a vec4 and passed the light value in place of the alpha which works fine. Based on other trials, as well as this, it's almost as if I can't have more than 3 attributes for some reason.

try using layout_location in shader code, opengl.org/wiki/Layout_Qualifier_(GLSL), layout(location = attribute index) in vec3 position; instead of glBindAttribLocation in code. — fen
Tried this as well. I also tried using glGetAttribLocation which gives me the same locations (0, 1, 2, 3) anyway. — VrydayVrything

Nicol Bolas Nicol Bolas · Accepted Answer · 2013-08-30T05:50:19

GL20.glLinkProgram(this.pId);

GL20.glBindAttribLocation(this.pId, 0, "in_Position");
GL20.glBindAttribLocation(this.pId, 1, "in_TextureCoord");
GL20.glBindAttribLocation(this.pId, 2, "in_Color");
GL20.glBindAttribLocation(this.pId, 3, "in_Light");

The glBindAttribLocation call needs to come before you link the program. Attribute locations are fixed at link time, so if you didn't bind any, OpenGL will arbitrarily assign them locations.

Trouble passing attributes to GLSL using LWJGL

2 Answers