Occlusion Query/Conditional Rendering

[gecko0307]

Conditional rendering is an OpenGL 3.x feature. The main idea behind it is rendering a simple bounding volume for object (like AABB) and testing if any of it is actually visible on screen. If it is, then we can render the object itself, but if it isn't, then we can safely discard the expensive rendering.

// Initialization:
GLuint query;
glGenQueries(1​, &query​);

// Rendering:
glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
glDepthMask(GL_FALSE);
glBeginQuery(GL_SAMPLES_PASSED, query);
// render bounding volume of an object
glEndQuery(GL_SAMPLES_PASSED);
glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
glDepthMask(GL_TRUE);

glBeginConditionalRender(query, GL_QUERY_WAIT​);
// render an object
glEndConditionalRender();

Conditional rendering can be an optional feature of Entity. This will require an additional interface on top of Drawable which defines AABB property.