From 9d56bc38a9037d63ae15cb9aa31e173b0b68e0fe Mon Sep 17 00:00:00 2001
From: Benjamin Otte <otte@redhat.com>
Date: Mon, 3 Jul 2023 05:55:21 +0200
Subject: [PATCH] Clear is_clear flag on unmap_image()

When a clear image surface gets mapped and the mapped image is modified,
the image surface needs to be marked as not clear.

Fixes early no-op exits from cairo_mask() etc when such an image was
then used as source or mask.

A new test map-clear-to-image is included.
---
 src/cairo-image-surface.c                 |   4 +++
 test/map-to-image.c                       |  38 ++++++++++++++++++++++
 test/reference/map-clear-to-image.ref.png | Bin 0 -> 100 bytes
 3 files changed, 42 insertions(+)
 create mode 100644 test/reference/map-clear-to-image.ref.png

diff --git a/src/cairo-image-surface.c b/src/cairo-image-surface.c
index 3b11eb981..0b5b8a88b 100644
--- a/src/cairo-image-surface.c
+++ b/src/cairo-image-surface.c
@@ -847,6 +847,10 @@ cairo_int_status_t
 _cairo_image_surface_unmap_image (void *abstract_surface,
 				  cairo_image_surface_t *image)
 {
+    cairo_image_surface_t *surface = abstract_surface;
+
+    surface->base.is_clear &= image->base.is_clear;
+
     cairo_surface_finish (&image->base);
     cairo_surface_destroy (&image->base);
 
diff --git a/test/map-to-image.c b/test/map-to-image.c
index 7fac9aa8a..0d18cbdd8 100644
--- a/test/map-to-image.c
+++ b/test/map-to-image.c
@@ -115,6 +115,38 @@ bit (cairo_t *cr, int width, int height)
     return CAIRO_TEST_SUCCESS;
 }
 
+static cairo_test_status_t
+clear (cairo_t *cr, int width, int height)
+{
+    cairo_surface_t *surface;
+    cairo_pattern_t *pattern;
+    cairo_rectangle_int_t extents;
+    cairo_t *cr2;
+
+    extents.x = extents.y = extents.width = extents.height = 1;
+
+    /* Fill background red */
+    cairo_set_source_rgb (cr, 1, 0, 0);
+    cairo_paint (cr);
+
+    /* Get clear image */
+    cairo_push_group (cr);
+
+    surface = cairo_surface_map_to_image (cairo_get_group_target (cr), &extents);
+    cr2 = cairo_create (surface);
+    cairo_set_source_rgb (cr2, 0, 0, 1);
+    cairo_paint (cr2);
+    cairo_destroy (cr2);
+    cairo_surface_unmap_image (cairo_get_group_target (cr), surface);
+
+    pattern = cairo_pop_group (cr);
+    /* all green */
+    cairo_set_source_rgb (cr, 0, 1, 0);
+    cairo_mask (cr, pattern);
+
+    return CAIRO_TEST_SUCCESS;
+}
+
 static cairo_test_status_t
 fill (cairo_t *cr, int width, int height)
 {
@@ -150,6 +182,12 @@ CAIRO_TEST (map_bit_to_image,
 	    "target=raster", /* requirements */
 	    WIDTH, HEIGHT,
 	    NULL, bit)
+CAIRO_TEST (map_clear_to_image,
+	    "Test mapping a clear surface to an image and modifying it externally marks it as not clear",
+	    "image", /* keywords */
+	    "target=raster", /* requirements */
+	    WIDTH, HEIGHT,
+	    NULL, clear)
 CAIRO_TEST (map_to_image_fill,
 	    "Test mapping a surface to an image and modifying it externally",
 	    "image", /* keywords */
diff --git a/test/reference/map-clear-to-image.ref.png b/test/reference/map-clear-to-image.ref.png
new file mode 100644
index 0000000000000000000000000000000000000000..846dbe28e55c5f078315a7c9b794c14391c8fb0a
GIT binary patch
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literal 0
HcmV?d00001