Unpremultiply cairo surface data.

1 files changed, 34 insertions, 3 deletions

diff --git a/pointer.c b/pointer.c
index 9571358..ec9f0a3 100644
--- a/pointer.c
+++ b/pointer.c
@@ -15,16 +15,48 @@
 static const char gem_device[] = "/dev/dri/card0";
 static const char socket_name[] = "\0wayland";
 
+static void
+unpremultiply_data(uint8_t *data, int width, int height, int stride)
+{
+	unsigned int i, j;
+	uint8_t *row;
+
+	for (j = 0; j < height; j++) {
+		row = data + j * stride;
+
+		for (i = 0; i < width; i++) {
+			uint8_t *b = &row[i * 4];
+			uint32_t pixel;
+			uint8_t  alpha;
+
+			memcpy (&pixel, b, sizeof (uint32_t));
+			alpha = (pixel & 0xff000000) >> 24;
+			if (alpha == 0) {
+				b[0] = b[1] = b[2] = b[3] = 0;
+			} else {
+				b[0] = (((pixel & 0xff0000) >> 16) * 255 + alpha / 2) / alpha;
+				b[1] = (((pixel & 0x00ff00) >>  8) * 255 + alpha / 2) / alpha;
+				b[2] = (((pixel & 0x0000ff) >>  0) * 255 + alpha / 2) / alpha;
+				b[3] = alpha;
+			}
+		}
+	}
+}
+
 static uint32_t name_cairo_surface(int fd, cairo_surface_t *surface)
 {
 	struct drm_i915_gem_create create;
 	struct drm_gem_flink flink;
 	struct drm_i915_gem_pwrite pwrite;
 	int32_t width, height, stride;
+	void *data;
 
 	width = cairo_image_surface_get_width(surface);
 	height = cairo_image_surface_get_height(surface);
 	stride = cairo_image_surface_get_stride(surface);
+	data = cairo_image_surface_get_data(surface);
+
+	unpremultiply_data(data, width, height, stride);
 
 	memset(&create, 0, sizeof(create));
 	create.size = height * stride;
@@ -37,8 +69,7 @@ static uint32_t name_cairo_surface(int fd, cairo_surface_t *surface)
 	pwrite.handle = create.handle;
 	pwrite.offset = 0;
 	pwrite.size = height * stride;
-	pwrite.data_ptr = (uint64_t) (uintptr_t)
-		cairo_image_surface_get_data(surface);
+	pwrite.data_ptr = (uint64_t) (uintptr_t) data;
 	if (ioctl(fd, DRM_IOCTL_I915_GEM_PWRITE, &pwrite) < 0) {
 		fprintf(stderr, "gem pwrite failed: %m\n");
 		return 0;
@@ -68,7 +99,7 @@ static uint32_t name_cairo_surface(int fd, cairo_surface_t *surface)
 static void *
 draw_pointer(int width, int height)
 {
-	const int d = 2, end = 4, tx = 2, ty = 6, dx = 5, dy = 4;
+	const int d = 2, end = 4, tx = 2, ty = 6, dx = 4, dy = 4;
 	cairo_surface_t *surface;
 	cairo_t *cr;