CODEWITHSUNDEEP
c++copenglglsl
PeddleSpam
PeddleSpam

Reputation: 438

Can a VBO be bound to multiple VAOs?

I'm trying to render a model's UV map by treating its texture coordinates as an array of vertex positions. I set up a VAO for the model which renders perfectly, then tried adding a second VAO and binding the texture coordinate buffer to it. Unfortunately it doesn't render anything.

I've written a second set of vertex and fragment shaders for the UV map which compile just fine. The buffer is bound in the same way as with the model VAO and the vertex attributes set. The only difference I can see is I'm not re-specifying the buffer data.

This is my code for setting up the model VAO:

// Create model VAO

glGenVertexArrays( 1, &modelVAO );
glBindVertexArray( modelVAO );

// Create position buffer

glGenBuffers( 1, &positionBuffer );
glBindBuffer( GL_ARRAY_BUFFER, positionBuffer );
glBufferData( GL_ARRAY_BUFFER, sizeof( GLfloat ) * vertexCount * 4, positions, GL_STATIC_DRAW );
glVertexAttribPointer( 0, 4, GL_FLOAT, GL_FALSE, 0, 0 );
glEnableVertexAttribArray( 0 );

// Create normal buffer

glGenBuffers( 1, &normalBuffer );
glBindBuffer( GL_ARRAY_BUFFER, normalBuffer );
glBufferData( GL_ARRAY_BUFFER, sizeof( GLfloat ) * vertexCount * 3, normals, GL_STATIC_DRAW );
glVertexAttribPointer( 1, 3, GL_FLOAT, GL_FALSE, 0, 0 );
glEnableVertexAttribArray( 1 );

// Create texture coordinate buffer

glGenBuffers( 1, &textureCoordinateBuffer );
glBindBuffer( GL_ARRAY_BUFFER, textureCoordinateBuffer );
glBufferData( GL_ARRAY_BUFFER, sizeof( GLfloat ) * vertexCount * 2, textureCoordinates, GL_DYNAMIC_DRAW );
glVertexAttribPointer( 2, 2, GL_FLOAT, GL_FALSE, 0, 0 );
glEnableVertexAttribArray( 2 );

// Unbind model VAO

glBindVertexArray( 0 );

Then I set up the UV map VAO like this:

// Create new UV map VAO

glGenVertexArrays( 1, &uvMapVAO );
glBindVertexArray( uvMapVAO );

// Bind texture coordinate buffer

glBindBuffer( GL_ARRAY_BUFFER, textureCoordinateBuffer );
glVertexAttribPointer( 0, 2, GL_FLOAT, GL_FALSE, 0, 0 );
glEnableVertexAttribArray( 0 );

// Unbind UV map VAO

glBindVertexArray( 0 );

Is it possible to use the same VBO with more than one VAO like this?

Upvotes: 6

Views: 2353

Answers (1)

Brett Hale
Brett Hale

Reputation: 22308

Yes. VAOs just store references to VBOs, with the associated data for format, offsets, etc., as specified by glVertexAttribPointer. Index VBOs have slightly different semantics.

Upvotes: 8

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