push_framebuffer

Redirects all subsequent drawing to the specified framebuffer.

This can either be an offscreen buffer created with Offscreen.to_texture or in the future it may be an onscreen framebuffer too.

You should understand that a framebuffer owns the following state:

• The projection matrix
• The modelview matrix stack
• The viewport
• The clip stack

So these items will automatically be saved and restored when you push and pop between different framebuffers.

Also remember a newly allocated framebuffer will have an identity matrix for the projection and modelview matrices which gives you a coordinate space like OpenGL with (-1, -1) corresponding to the top left of the viewport, (1, 1) corresponding to the bottom right and +z coming out towards the viewer.

If you want to set up a coordinate space like Clutter does with (0, 0) corresponding to the top left and (framebuffer_width, framebuffer_height) corresponding to the bottom right you can do so like this:

static void
setup_viewport (unsigned int width,
								unsigned int height,
								float fovy,
								float aspect,
								float z_near,
								float z_far)
{
	float z_camera;
	CoglMatrix projection_matrix;
	CoglMatrix mv_matrix;

	cogl_set_viewport (0, 0, width, height);
	cogl_perspective (fovy, aspect, z_near, z_far);

	cogl_get_projection_matrix (&projection_matrix);
	z_camera = 0.5 * projection_matrix.xx;

	cogl_matrix_init_identity (&mv_matrix);
	cogl_matrix_translate (&mv_matrix, -0.5f, -0.5f, -z_camera);
	cogl_matrix_scale (&mv_matrix, 1.0f / width, -1.0f / height, 1.0f / width);
	cogl_matrix_translate (&mv_matrix, 0.0f, -1.0 * height, 0.0f);
	cogl_set_modelview_matrix (&mv_matrix);
}

static void
my_init_framebuffer (ClutterStage *stage,
										 CoglFramebuffer *framebuffer,
										 unsigned int framebuffer_width,
										 unsigned int framebuffer_height)
{
	ClutterPerspective perspective;

	clutter_stage_get_perspective (stage, &perspective);

	cogl_push_framebuffer (framebuffer);
	setup_viewport (framebuffer_width,
									framebuffer_height,
									perspective.fovy,
									perspective.aspect,
									perspective.z_near,
									perspective.z_far);
}

The previous framebuffer can be restored by calling pop_framebuffer

Parameters:

buffer

A Framebuffer object, either onscreen or offscreen.