cogl_offscreen_new_with_texture ()

CoglOffscreen *
cogl_offscreen_new_with_texture (CoglTexture *texture);

This creates an offscreen framebuffer object using the given texture as the primary color buffer. It doesn't just initialize the contents of the offscreen buffer with the texture ; they are tightly bound so that drawing to the offscreen buffer effectively updates the contents of the given texture. You don't need to destroy the offscreen buffer before you can use the texture again.

The storage for the framebuffer is actually allocated lazily so this function will never return NULL to indicate a runtime error. This means it is still possible to configure the framebuffer before it is really allocated.

Simple applications without full error handling can simply rely on Cogl to lazily allocate the storage of framebuffers but you should be aware that if Cogl encounters an error (such as running out of GPU memory) then your application will simply abort with an error message. If you need to be able to catch such exceptions at runtime then you can explicitly allocate your framebuffer when you have finished configuring it by calling cogl_framebuffer_allocate() and passing in a CoglError argument to catch any exceptions.

cogl_offscreen_new_to_texture ()

CoglOffscreen *
cogl_offscreen_new_to_texture (CoglTexture *texture);

This creates an offscreen buffer object using the given texture as the primary color buffer. It doesn't just initialize the contents of the offscreen buffer with the texture ; they are tightly bound so that drawing to the offscreen buffer effectivly updates the contents of the given texture. You don't need to destroy the offscreen buffer before you can use the texture again.

cogl_is_offscreen ()

CoglBool
cogl_is_offscreen (void *object);

Determines whether the given CoglObject references an offscreen framebuffer object.

cogl_set_framebuffer ()

void
cogl_set_framebuffer (CoglFramebuffer *buffer);

This redirects all subsequent drawing to the specified framebuffer. This can either be an offscreen buffer created with cogl_offscreen_new_to_texture() or in the future it may be an onscreen framebuffers too.

Since: 1.2

cogl_push_framebuffer ()

void
cogl_push_framebuffer (CoglFramebuffer *buffer);

Redirects all subsequent drawing to the specified framebuffer. This can either be an offscreen buffer created with cogl_offscreen_new_to_texture() or in the future it may be an onscreen framebuffer too.

You should understand that a framebuffer owns the following state:

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:

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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 cogl_pop_framebuffer()

Since: 1.2

cogl_pop_framebuffer ()

void
cogl_pop_framebuffer (void);

Restores the framebuffer that was previously at the top of the stack. All subsequent drawing will be redirected to this framebuffer.

Since: 1.2

cogl_set_draw_buffer ()

void
cogl_set_draw_buffer (CoglBufferTarget target,
                      CoglHandle offscreen);

Redirects all subsequent drawing to the specified framebuffer. This can either be an offscreen buffer created with cogl_offscreen_new_to_texture() or you can revert to your original on screen window buffer.

cogl_pop_draw_buffer ()

void
cogl_pop_draw_buffer (void);

Restore cogl_set_draw_buffer() state.

cogl_push_draw_buffer ()

void
cogl_push_draw_buffer (void);

Save cogl_set_draw_buffer() state.