Sending data to a shader using per vertex attributes and VBOs - Fish-In-A-Suit/Conquest GitHub Wiki

Per vertex attributes are declared with the keyword in (inside a shader written in GLSL). Data for tgese attributes must be supplied by the "main source code" - the game engine.

//vertex shader
#version 400

in vec3 VertexPosition;
in vec3 VertexColour;

out vec3 Colour;

void main() {
    Colour = VertexColour;
    gl_Position = vec4(VertexPosition, 1)
    //gl_Position is a built-in output variable
}

//fragment shader
#version 400

in vec3 Colour;

out vec4 FragColour;

void main() {
    FragColour = vec4(Colour, 1);
}

1. Define the mapping prior to linking the program

glBindAttribLocation(programID, 0, "VertexPosition")
glBindAttribLocation(programID, 0, "VertexColour")

2. Create the VAO

int vaoID = glGenVertexArrays();

3. Create and populate vertex buffer objects for each attribute

float[] positionData = {
    -0.5f, 0.5f, 0f,
    -0.5f, -0.5f, 0f,
            
     0.5f, -0.5f, 0f,
     0.5f, 0.5f, 0f
};

int[] indices = {
    0, 1, 3, //top left triangle (V0, V1, V3)
    3, 1, 2 //bottom right triangle (V3, V1, V2)
};

float[] colourData = {
    1.0f, 0.0f, 0.0f,
    0.0f, 1.0f, 0.0f,
    0.0f, 0.0f, 1.0f,
    1.0f, 1.0f, 0.0f
};

4. Transform the array data to corresponding array type

FloatBuffer positionBuffer = BufferUtils.createFloatBuffer(positionData.length);
positionBuffer.put(positionData).flip();

IntBuffer indicesBuffer = BufferUtils.createIntBuffer(indices.length);
indicesBuffer.put(indices).flip();

FloatBuffer colourBuffer = BufferUtils.createFloatBuffer(colourData.length);
colourBuffer.put(colourData).flip();

5. Create and populate vertex buffer objects for each attribute

posVboID = glGenBuffers();
glBindBuffer(GL_ARRAY_BUFFER, posVboID);
glBufferData(GL_ARRAY_BUFFER, positionBuffer, GL_STATIC_DRAW);

colourVboID = glGenBuffers();
glBindBuffer(GL_ARRAY_BUFFER, colourVboID);
glBufferData(GL_ARRAY_BUFFER, colourBuffer, GL_STATIC_DRAW);

indicesVboID = glGenBuffers();
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indicesVboID);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, indicesBuffer, GL_STATIC_DRAW);

The target GL_ARRAY_BUFFER is used whenever storing vertex attribute data.

6. Create and bind to a vertex array object, which stores the relationship between the buffers and the input attributes

glBindVertexArray(vaoID);

glEnableVertexAttribArray(0); //position
glEnableVertexAttribArray(1); //colour

glBindBuffer(GL_ARRAY_BUFFER, positionsVboID);
glVertexAttribPointer(0, 3, GL_, false, 0, 0);

glBindBuffer(GL_ARRAY_BUFFER, colourVboID);
glVertexAttribPointer(0, 3, GL_FLOAT, false, 0, 0);

7. In the render function, bind the vao and the indices vbo and call glDrawElements:

glBindVertexArray(vaoID);
glEnableVertexAttribArray(0);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, mesh.getIndicesVboID());

glDrawElements(GL_TRIANGLES, positionData.length, GL_UNSIGNED_INT, 0);