cogl-framebuffer: Add _cogl_blit_framebuffer
This adds the _cogl_blit_framebuffer internal function which is a wrapper around glBlitFramebuffer. The API is changed from the GL version of the function to reflect the limitations provided by the GL_ANGLE_framebuffer_blit extension (eg, no scaling or mirroring).
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Neil Roberts
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2 changed files with 99 additions and 0 deletions
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@ -288,5 +288,58 @@ void
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_cogl_push_framebuffers (CoglFramebuffer *draw_buffer,
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CoglFramebuffer *read_buffer);
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/*
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* _cogl_blit_framebuffer:
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* @src_x: Source x position
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* @src_y: Source y position
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* @dst_x: Destination x position
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* @dst_y: Destination y position
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* @width: Width of region to copy
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* @height: Height of region to copy
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*
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* This blits a region of the color buffer of the current draw buffer
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* to the current read buffer. The draw and read buffers can be set up
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* using _cogl_push_framebuffers(). This function should only be
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* called if the COGL_FEATURE_OFFSCREEN_BLIT feature is
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* advertised. The two buffers must both be offscreen and have the
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* same format.
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*
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* Note that this function differs a lot from the glBlitFramebuffer
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* function provided by the GL_EXT_framebuffer_blit extension. Notably
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* it doesn't support having different sizes for the source and
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* destination rectangle. This isn't supported by the corresponding
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* GL_ANGLE_framebuffer_blit extension on GLES2.0 and it doesn't seem
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* like a particularly useful feature. If the application wanted to
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* scale the results it may make more sense to draw a primitive
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* instead.
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*
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* We can only really support blitting between two offscreen buffers
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* for this function on GLES2.0. This is because we effectively render
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* upside down to offscreen buffers to maintain Cogl's representation
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* of the texture coordinate system where 0,0 is the top left of the
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* texture. If we were to blit from an offscreen to an onscreen buffer
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* then we would need to mirror the blit along the x-axis but the GLES
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* extension does not support this.
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*
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* The GL function is documented to be affected by the scissor. This
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* function therefore ensure that an empty clip stack is flushed
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* before performing the blit which means the scissor is effectively
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* ignored.
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*
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* The function also doesn't support specifying the buffers to copy
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* and instead only the color buffer is copied. When copying the depth
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* or stencil buffers the extension on GLES2.0 only supports copying
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* the full buffer which would be awkward to document with this
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* API. If we wanted to support that feature it may be better to have
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* a separate function to copy the entire buffer for a given mask.
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*/
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void
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_cogl_blit_framebuffer (unsigned int src_x,
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unsigned int src_y,
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unsigned int dst_x,
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unsigned int dst_y,
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unsigned int width,
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unsigned int height);
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#endif /* __COGL_FRAMEBUFFER_PRIVATE_H */
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@ -54,6 +54,8 @@
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#endif
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#define glBlitFramebuffer ctx->drv.pf_glBlitFramebuffer
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#ifndef GL_FRAMEBUFFER
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#define GL_FRAMEBUFFER 0x8D40
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#endif
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@ -1429,3 +1431,47 @@ _cogl_framebuffer_try_fast_read_pixel (CoglFramebuffer *framebuffer,
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return FALSE;
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}
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void
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_cogl_blit_framebuffer (unsigned int src_x,
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unsigned int src_y,
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unsigned int dst_x,
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unsigned int dst_y,
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unsigned int width,
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unsigned int height)
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{
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CoglFramebuffer *draw_buffer;
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CoglFramebuffer *read_buffer;
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_COGL_GET_CONTEXT (ctx, NO_RETVAL);
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draw_buffer = _cogl_get_draw_buffer ();
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read_buffer = _cogl_get_read_buffer ();
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g_return_if_fail (cogl_features_available (COGL_FEATURE_OFFSCREEN_BLIT));
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/* We can only support blitting between offscreen buffers because
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otherwise we would need to mirror the image and GLES2.0 doesn't
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support this */
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g_return_if_fail (cogl_is_offscreen (draw_buffer));
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g_return_if_fail (cogl_is_offscreen (read_buffer));
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/* The buffers must be the same format */
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g_return_if_fail (draw_buffer->format == read_buffer->format);
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/* Make sure the current framebuffers are bound. We explicitly avoid
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flushing the clip state so we can bind our own empty state */
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_cogl_framebuffer_flush_state (_cogl_get_draw_buffer (),
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_cogl_get_read_buffer (),
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COGL_FRAMEBUFFER_FLUSH_SKIP_CLIP_STATE);
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/* Flush any empty clip stack because glBlitFramebuffer is affected
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by the scissor and we want to hide this feature for the Cogl API
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because it's not obvious to an app how the clip state will affect
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the scissor */
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_cogl_clip_stack_flush (NULL);
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glBlitFramebuffer (src_x, src_y,
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src_x + width, src_y + height,
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dst_x, dst_y,
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dst_x + width, dst_y + height,
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GL_COLOR_BUFFER_BIT,
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GL_NEAREST);
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}
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