CODEWITHSUNDEEP
opengl-esopengl-es-2.0vertex
KomodoDave
KomodoDave

Reputation: 7319

OpenGL ES 2.0: Using glBufferData with new vertex data size

I have an array of vertex attributes GLfloat *vxData. I've bound both GL_ARRAY_BUFFER and GL_ELEMENT_ARRAY_BUFFER with vxData and the correct index data, and the initial vertices render successfully.

At each render step I do:

glBindBuffer(GL_ARRAY_BUFFER, buffers[0]);
glBufferData(GL_ARRAY_BUFFER, vxDataSize, vxData, GL_STATIC_DRAW);
glDrawElements(...)

At some stage, vxData changes size to accommodate fewer/more vertices, the index data is recreated to reflect this, and vxDataSize is updated. For the render immediately following this change in data, is it correct to simply call the same lines above?

I'm aware of alternative possibilities e.g. using glMapBufferOES, I'd simply like to know whether the above is technically correct for this scenario.

Upvotes: 1

Views: 2186

Answers (1)

Nicol Bolas
Nicol Bolas

Reputation: 473407

Is it correct? Yes, you can do that and you should get functional code that renders what you expect it to. Is it good?

No.

First, you're lying to the OpenGL implementation. You told it that you were making STATIC data. STATIC means you upload to it once. If you're doing that every frame, then you should be using STREAM, not STATIC.

Second, you should not be making buffers bigger and smaller. It's one thing to flush the old data out, but if you're telling OpenGL that the buffer needs to be bigger, then it has to actually allocate memory. That's not good. Pick a size and stick with it. Pick the largest size you can expect to use and stay there.

Upvotes: 5

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