cogl: Expose cogl_blit_framebuffer

The function will be used in copying from a primary GPU framebuffer to a
secondary GPU framebuffer using the primary GPU specifically when the
secondary GPU is not render-capable.

To allow falling back in case glBlitFramebuffer cannot be used, add boolean
return value, and GError argument for debugging purposes.

https://gitlab.gnome.org/GNOME/mutter/merge_requests/615

cogl/cogl/cogl-blit.c

@@ -207,11 +207,12 @@ _cogl_blit_framebuffer_blit (CoglBlitData *data,
                              int width,
                              int height)
 {
-  _cogl_blit_framebuffer (data->src_fb,
+  cogl_blit_framebuffer (data->src_fb,
                          data->dest_fb,
                          src_x, src_y,
                          dst_x, dst_y,
-                          width, height);
+                         width, height,
+                         NULL);
 }
 
 static void

cogl/cogl/cogl-framebuffer-private.h

@@ -364,61 +364,6 @@ void
 _cogl_push_framebuffers (CoglFramebuffer *draw_buffer,
                          CoglFramebuffer *read_buffer);
 
-/*
- * _cogl_blit_framebuffer:
- * @src: The source #CoglFramebuffer
- * @dest: The destination #CoglFramebuffer
- * @src_x: Source x position
- * @src_y: Source y position
- * @dst_x: Destination x position
- * @dst_y: Destination y position
- * @width: Width of region to copy
- * @height: Height of region to copy
- *
- * This blits a region of the color buffer of the source buffer
- * to the destination buffer. This function should only be
- * called if the COGL_PRIVATE_FEATURE_BLIT_FRAMEBUFFER feature is
- * advertised.
- *
- * The source and destination rectangles are defined in offscreen
- * framebuffer orientation. When copying between an offscreen and
- * onscreen framebuffers, the image is y-flipped accordingly.
- *
- * The two buffers must have the same value types (e.g. floating-point,
- * unsigned int, signed int, or fixed-point), but color formats do not
- * need to match. This limitation comes from OpenGL ES 3.0 definition
- * of glBlitFramebuffer.
- *
- * Note that this function differs a lot from the glBlitFramebuffer
- * function provided by the GL_EXT_framebuffer_blit extension. Notably
- * it doesn't support having different sizes for the source and
- * destination rectangle. This doesn't seem
- * like a particularly useful feature. If the application wanted to
- * scale the results it may make more sense to draw a primitive
- * instead.
- *
- * The GL function is documented to be affected by the scissor. This
- * function therefore ensure that an empty clip stack is flushed
- * before performing the blit which means the scissor is effectively
- * ignored.
- *
- * The function also doesn't support specifying the buffers to copy
- * and instead only the color buffer is copied. When copying the depth
- * or stencil buffers the extension on GLES2.0 only supports copying
- * the full buffer which would be awkward to document with this
- * API. If we wanted to support that feature it may be better to have
- * a separate function to copy the entire buffer for a given mask.
- */
-void
-_cogl_blit_framebuffer (CoglFramebuffer *src,
-                        CoglFramebuffer *dest,
-                        int src_x,
-                        int src_y,
-                        int dst_x,
-                        int dst_y,
-                        int width,
-                        int height);
-
 void
 _cogl_framebuffer_push_projection (CoglFramebuffer *framebuffer);
 

cogl/cogl/cogl-framebuffer.c

@@ -1341,26 +1341,38 @@ cogl_framebuffer_read_pixels (CoglFramebuffer *framebuffer,
   return ret;
 }
 
-void
+gboolean
-_cogl_blit_framebuffer (CoglFramebuffer *src,
+cogl_blit_framebuffer (CoglFramebuffer *src,
                        CoglFramebuffer *dest,
                        int src_x,
                        int src_y,
                        int dst_x,
                        int dst_y,
                        int width,
-                        int height)
+                       int height,
+                       GError **error)
 {
   CoglContext *ctx = src->context;
   int src_x1, src_y1, src_x2, src_y2;
   int dst_x1, dst_y1, dst_x2, dst_y2;
 
-  g_return_if_fail (_cogl_has_private_feature
+  if (!_cogl_has_private_feature (ctx, COGL_PRIVATE_FEATURE_BLIT_FRAMEBUFFER))
-                    (ctx, COGL_PRIVATE_FEATURE_BLIT_FRAMEBUFFER));
+    {
+      g_set_error_literal (error, COGL_SYSTEM_ERROR,
+                           COGL_SYSTEM_ERROR_UNSUPPORTED,
+                           "Cogl BLIT_FRAMEBUFFER is not supported by the system.");
+      return FALSE;
+    }
 
   /* The buffers must use the same premult convention */
-  g_return_if_fail ((src->internal_format & COGL_PREMULT_BIT) ==
+  if ((src->internal_format & COGL_PREMULT_BIT) !=
-                    (dest->internal_format & COGL_PREMULT_BIT));
+      (dest->internal_format & COGL_PREMULT_BIT))
+    {
+      g_set_error_literal (error, COGL_SYSTEM_ERROR,
+                           COGL_SYSTEM_ERROR_UNSUPPORTED,
+                           "cogl_blit_framebuffer premult mismatch.");
+      return FALSE;
+    }
 
   /* Make sure the current framebuffers are bound. We explicitly avoid
      flushing the clip state so we can bind our own empty state */
@@ -1418,6 +1430,8 @@ _cogl_blit_framebuffer (CoglFramebuffer *src,
                           dst_x1, dst_y1, dst_x2, dst_y2,
                           GL_COLOR_BUFFER_BIT,
                           GL_NEAREST);
+
+  return TRUE;
 }
 
 void

cogl/cogl/cogl-framebuffer.h

@@ -3,7 +3,8 @@
  *
  * A Low Level GPU Graphics and Utilities API
  *
- * Copyright (C) 2011 Intel Corporation.
+ * Copyright (C) 2007,2008,2009,2011 Intel Corporation.
+ * Copyright (C) 2019 DisplayLink (UK) Ltd.
  *
  * Permission is hereby granted, free of charge, to any person
  * obtaining a copy of this software and associated documentation
@@ -1797,6 +1798,69 @@ typedef enum /*< prefix=COGL_FRAMEBUFFER_ERROR >*/
 gboolean
 cogl_is_framebuffer (void *object);
 
+/**
+ * cogl_blit_framebuffer:
+ * @src: The source #CoglFramebuffer
+ * @dest: The destination #CoglFramebuffer
+ * @src_x: Source x position
+ * @src_y: Source y position
+ * @dst_x: Destination x position
+ * @dst_y: Destination y position
+ * @width: Width of region to copy
+ * @height: Height of region to copy
+ * @error: optional error object
+ *
+ * @return FALSE for an immediately detected error, TRUE otherwise.
+ *
+ * This blits a region of the color buffer of the source buffer
+ * to the destination buffer. This function should only be
+ * called if the COGL_PRIVATE_FEATURE_BLIT_FRAMEBUFFER feature is
+ * advertised.
+ *
+ * The source and destination rectangles are defined in offscreen
+ * framebuffer orientation. When copying between an offscreen and
+ * onscreen framebuffers, the image is y-flipped accordingly.
+ *
+ * The two buffers must have the same value types (e.g. floating-point,
+ * unsigned int, signed int, or fixed-point), but color formats do not
+ * need to match. This limitation comes from OpenGL ES 3.0 definition
+ * of glBlitFramebuffer.
+ *
+ * Note that this function differs a lot from the glBlitFramebuffer
+ * function provided by the GL_EXT_framebuffer_blit extension. Notably
+ * it doesn't support having different sizes for the source and
+ * destination rectangle. This doesn't seem
+ * like a particularly useful feature. If the application wanted to
+ * scale the results it may make more sense to draw a primitive
+ * instead.
+ *
+ * The GL function is documented to be affected by the scissor. This
+ * function therefore ensure that an empty clip stack is flushed
+ * before performing the blit which means the scissor is effectively
+ * ignored.
+ *
+ * The function also doesn't support specifying the buffers to copy
+ * and instead only the color buffer is copied. When copying the depth
+ * or stencil buffers the extension on GLES2.0 only supports copying
+ * the full buffer which would be awkward to document with this
+ * API. If we wanted to support that feature it may be better to have
+ * a separate function to copy the entire buffer for a given mask.
+ *
+ * The @c error argument is optional, it can be NULL. If it is not NULL
+ * and this function returns FALSE, an error object with a code from
+ * COGL_SYSTEM_ERROR will be created.
+ */
+gboolean
+cogl_blit_framebuffer (CoglFramebuffer *src,
+                       CoglFramebuffer *dest,
+                       int src_x,
+                       int src_y,
+                       int dst_x,
+                       int dst_y,
+                       int width,
+                       int height,
+                       GError **error);
+
 G_END_DECLS
 
 #endif /* __COGL_FRAMEBUFFER_H */