VAO Reference Behavior
- VAO keeps references to all the vertex attribute configurations set while it is bound.
- You can link multiple VBOs to a VAO using different attribute indices.
- However, only one EBO can be bound to a VAO at a time. The VAO remembers the EBO bound at the moment of setup.
Setup
Below is a typical setup phase for a VAO with multiple VBOs and a single EBO:
java
vaoID = GL30.glGenVertexArrays();
GL30.glBindVertexArray(vaoID);
// bind the first VBO and configure attribute 0
// this gets recorded in the VAO
GL15.glBindBuffer(GL15.GL_ARRAY_BUFFER, vboID_0);
GL20.glVertexAttribPointer(0, ...);
GL20.glEnableVertexAttribArray(0);
GL33.glVertexAttribDivisor(0, divisor); // optional: if you want instancing
// bind the second VBO and configure attribute 1
GL15.glBindBuffer(GL15.GL_ARRAY_BUFFER, vboID_1);
GL20.glVertexAttribPointer(1, ...);
GL20.glEnableVertexAttribArray(1);
GL33.glVertexAttribDivisor(1, divisor);
// bind EBO
// this gets recorded in the VAO
GL15.glBindBuffer(GL15.GL_ELEMENT_ARRAY_BUFFER, eboID);
// VAO setup is done
// unbind if necessary
GL30.glBindVertexArray(0); // bind to 0 or the prev binding depends on your need
GL15.glBindBuffer(GL15.GL_ARRAY_BUFFER, 0);
GL15.glBindBuffer(GL15.GL_ELEMENT_ARRAY_BUFFER, 0);Draw Phase
To draw with the previously configured VAO and everything, all you need to do is re-bind the VAO:
java
GL30.glBindVertexArray(vaoID);
GL11.glDrawElements(...); // or any other variant draw callsNotice:
DrawArraysseries draw calls don't require an EBO to guide the drawing process.DrawElementsseries draw calls do require an EBO for drawing.- It's preferred to use
DrawElementswhen vertex reuse is necessarily, which is most of the scenarios.
For GL11.glDrawElements(GL11.GL_TRIANGLES, count, GL11.GL_UNSIGNED_INT, offset)
GL_TRIANGLESrepresents the primitive typecountrepresents the number of indicesGL11.GL_UNSIGNED_INTrepresents how GPU interprets the EBO (e.g. every index is a 32-bit unsigned integer; you could use short or byte too)offsetrepresents the reading offset of the EBO in bytes
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