Optimize imageviewer xcb_clear_area calls
diff --git a/example/imageviewer/imageviewer.cc b/example/imageviewer/imageviewer.cc
index de73643..5fc8b04 100644
--- a/example/imageviewer/imageviewer.cc
+++ b/example/imageviewer/imageviewer.cc
@@ -490,11 +490,35 @@
return true;
}
+bool //
+intersects(int32_t old_x,
+ int32_t old_y,
+ int32_t width,
+ int32_t height,
+ int32_t new_x,
+ int32_t new_y) {
+ if ((width <= 0) || (height <= 0)) {
+ return false;
+ } else if ((old_x > new_x) && ((old_x - new_x) >= width)) {
+ return false;
+ } else if ((new_x > old_x) && ((new_x - old_x) >= width)) {
+ return false;
+ } else if ((old_y > new_y) && ((old_y - new_y) >= height)) {
+ return false;
+ } else if ((new_y > old_y) && ((new_y - old_y) >= height)) {
+ return false;
+ }
+ return true;
+}
+
// clear_area clears the L-shaped difference between old and new rectangles (of
// equal width and height). It does this in up to two xcb_clear_area calls,
// labeled A and B in the example below (with old_x=0, old_y=0, width=5,
// height=4, new_x=2, new_y=2).
//
+// If the old and new rectangles do not intersect then the old rectangle (not
+// an L-shape) will be cleared.
+//
// AAAAA
// AAAAA
// BB+---+
@@ -510,6 +534,13 @@
int32_t height,
int32_t new_x,
int32_t new_y) {
+ if ((width <= 0) || (height <= 0)) {
+ return;
+ } else if (!intersects(old_x, old_y, width, height, new_x, new_y)) {
+ xcb_clear_area(c, 1, w, old_x, old_y, width, height);
+ return;
+ }
+
int32_t dy = new_y - old_y;
if (dy < 0) {
xcb_clear_area(c, 1, w, old_x, old_y + height + dy, width, -dy);
