[debug] Check image contents using memcheck.

As an aide to tracking down the source of uninitialised reads, run
VALGRIND_CHECK_MEM_IS_DEFINED() over the contents of image surfaces at the
boundary between backends, e.g. upon setting a glyph image or acquiring
a source image.

src/cairo-debug.c

@@ -77,3 +77,45 @@ cairo_debug_reset_static_data (void)
 
     CAIRO_MUTEX_FINALIZE ();
 }
+
+#if HAVE_VALGRIND
+#include <memcheck.h>
+
+void
+_cairo_debug_check_image_surface_is_defined (const cairo_surface_t *surface)
+{
+    const cairo_image_surface_t *image = (cairo_image_surface_t *) surface;
+    const uint8_t *bits;
+    int row, width;
+
+    if (surface == NULL)
+	return;
+
+    if (! RUNNING_ON_VALGRIND)
+	return;
+
+    bits = image->data;
+    switch (image->format) {
+    case CAIRO_FORMAT_A1:
+	width = (image->width + 7)/8;
+	break;
+    case CAIRO_FORMAT_A8:
+	width = image->width;
+	break;
+    case CAIRO_FORMAT_RGB24:
+    case CAIRO_FORMAT_ARGB32:
+	width = image->width*4;
+	break;
+    default:
+	ASSERT_NOT_REACHED;
+	return;
+    }
+
+    for (row = 0; row < image->height; row++) {
+	VALGRIND_CHECK_MEM_IS_DEFINED (bits, width);
+	/* and then silence any future valgrind warnings */
+	VALGRIND_MAKE_MEM_DEFINED (bits, width);
+	bits += image->stride;
+    }
+}
+#endif

src/cairo-ft-font.c

@@ -996,6 +996,8 @@ _get_bitmap_surface (FT_Bitmap		     *bitmap,
 
     _cairo_image_surface_assume_ownership_of_data ((*surface));
 
+    _cairo_debug_check_image_surface_is_defined (&(*surface)->base);
+
     return CAIRO_STATUS_SUCCESS;
 }
 

src/cairo-pattern.c

@@ -1452,6 +1452,8 @@ _cairo_pattern_acquire_surface_for_gradient (const cairo_gradient_pattern_t *pat
 
     pixman_image_unref (pixman_image);
 
+    _cairo_debug_check_image_surface_is_defined (&image->base);
+
     status = _cairo_surface_clone_similar (dst, &image->base,
 					   opaque ?
 					   CAIRO_CONTENT_COLOR :

src/cairo-png.c

@@ -654,6 +654,8 @@ read_png (struct png_read_closure_t *png_closure)
     _cairo_image_surface_assume_ownership_of_data ((cairo_image_surface_t*)surface);
     data = NULL;
 
+    _cairo_debug_check_image_surface_is_defined (surface);
+
     status = _cairo_memory_stream_destroy (png_closure->png_data,
 					   &mime_data,
 					   &mime_data_length);

src/cairo-scaled-font.c

@@ -2409,6 +2409,9 @@ _cairo_scaled_glyph_set_surface (cairo_scaled_glyph_t *scaled_glyph,
 {
     if (scaled_glyph->surface != NULL)
 	cairo_surface_destroy (&scaled_glyph->surface->base);
+
+    /* sanity check the backend glyph contents */
+    _cairo_debug_check_image_surface_is_defined (&surface->base);
     scaled_glyph->surface = surface;
 }
 

src/cairo-surface.c

@@ -1153,6 +1153,8 @@ _cairo_surface_acquire_source_image (cairo_surface_t         *surface,
 				     cairo_image_surface_t  **image_out,
 				     void                   **image_extra)
 {
+    cairo_status_t status;
+
     if (surface->status)
 	return surface->status;
 
@@ -1161,9 +1163,14 @@ _cairo_surface_acquire_source_image (cairo_surface_t         *surface,
     if (surface->backend->acquire_source_image == NULL)
 	return CAIRO_INT_STATUS_UNSUPPORTED;
 
-    return _cairo_surface_set_error (surface,
-	    surface->backend->acquire_source_image (surface,
-						    image_out, image_extra));
+    status = surface->backend->acquire_source_image (surface,
+						     image_out, image_extra);
+    if (unlikely (status))
+	return _cairo_surface_set_error (surface, status);
+
+    _cairo_debug_check_image_surface_is_defined (&(*image_out)->base);
+
+    return CAIRO_STATUS_SUCCESS;
 }
 
 /**
@@ -1222,6 +1229,8 @@ _cairo_surface_acquire_dest_image (cairo_surface_t         *surface,
 				   cairo_rectangle_int_t   *image_rect,
 				   void                   **image_extra)
 {
+    cairo_status_t status;
+
     if (surface->status)
 	return surface->status;
 
@@ -1230,12 +1239,17 @@ _cairo_surface_acquire_dest_image (cairo_surface_t         *surface,
     if (surface->backend->acquire_dest_image == NULL)
 	return CAIRO_INT_STATUS_UNSUPPORTED;
 
-    return _cairo_surface_set_error (surface,
-	    surface->backend->acquire_dest_image (surface,
-						  interest_rect,
-						  image_out,
-						  image_rect,
-						  image_extra));
+    status = surface->backend->acquire_dest_image (surface,
+						   interest_rect,
+						   image_out,
+						   image_rect,
+						   image_extra);
+    if (unlikely (status))
+	return _cairo_surface_set_error (surface, status);
+
+    _cairo_debug_check_image_surface_is_defined (&(*image_out)->base);
+
+    return CAIRO_STATUS_SUCCESS;
 }
 
 /**

src/cairoint.h

@@ -2741,4 +2741,15 @@ CAIRO_END_DECLS
 #include "cairo-malloc-private.h"
 #include "cairo-hash-private.h"
 
+#if HAVE_VALGRIND
+
+cairo_private void
+_cairo_debug_check_image_surface_is_defined (const cairo_surface_t *surface);
+
+#else
+
+#define _cairo_debug_check_image_surface_is_defined(X)
+
+#endif
+
 #endif