[client] round overlay damage outward

Expand ImGui window damage to include its border and round both logical
window bounds and framebuffer-scaled bounds outward.

This prevents a one-pixel strip of stale desktop content when an
overlay window is resized at fractional positions or display scales.

client/src/app.c

@@ -30,6 +30,7 @@
 #include "kb.h"
 
 #include "common/debug.h"
+#include "common/rects.h"
 #include "common/stringutils.h"
 #include "interface/overlay.h"
 #include "overlays.h"
@@ -1073,12 +1074,7 @@ render_again:
           buffer, MAX_OVERLAY_RECTS);
 
     for (int i = 0; i < written; ++i)
-    {
+      rectScaleOutward(buffer + i, g_state.windowScale);
-      buffer[i].x *= g_state.windowScale;
-      buffer[i].y *= g_state.windowScale;
-      buffer[i].w *= g_state.windowScale;
-      buffer[i].h *= g_state.windowScale;
-    }
 
     // It is an error to run out of rectangles, because we will not be able to
     // correctly calculate the damage of the next frame.

client/src/overlay_utils.c

@@ -20,6 +20,7 @@
 
 #include "overlay_utils.h"
 
+#include <math.h>
 #include <string.h>
 
 #include "common/open.h"
@@ -41,13 +42,19 @@
 
 void overlayGetImGuiRect(struct Rect * rect)
 {
-  ImVec2 pos  = igGetWindowPos();
+  const ImVec2 pos    = igGetWindowPos();
-  ImVec2 size = igGetWindowSize();
+  const ImVec2 size   = igGetWindowSize();
+  const float  border = igGetStyle()->WindowBorderSize;
+  const float  margin = border > 1.0f ? border : 1.0f;
+  const int    left   = (int)floorf(pos.x - margin);
+  const int    top    = (int)floorf(pos.y - margin);
+  const int    right  = (int)ceilf(pos.x + size.x + margin);
+  const int    bottom = (int)ceilf(pos.y + size.y + margin);
 
-  rect->x = pos.x;
+  rect->x = left;
-  rect->y = pos.y;
+  rect->y = top;
-  rect->w = size.x;
+  rect->w = right  - left;
-  rect->h = size.y;
+  rect->h = bottom - top;
 }
 
 ImVec2 * overlayGetScreenSize(void)

common/include/common/rects.h

@@ -31,6 +31,8 @@ extern void (*rectCopyUnaligned)(
     uint8_t *restrict dst, const uint8_t *restrict src,
     int ystart, int yend, int dx, int dstPitch, int srcPitch, int width);
 
+void rectScaleOutward(struct Rect * rect, double scale);
+
 void rectsBufferToFramebuffer(FrameDamageRect * rects, int count, int bpp,
   FrameBuffer * frame, int dstPitch, int height,
   const uint8_t * src, int srcPitch);

common/src/rects.c

@@ -22,6 +22,7 @@
 #include "common/util.h"
 #include "common/cpuinfo.h"
 
+#include <math.h>
 #include <stdlib.h>
 #include <immintrin.h>
 
@@ -38,6 +39,19 @@ struct Edge
   int delta;
 };
 
+void rectScaleOutward(struct Rect * rect, double scale)
+{
+  const int left   = (int)floor(rect->x * scale);
+  const int top    = (int)floor(rect->y * scale);
+  const int right  = (int)ceil(((double)rect->x + rect->w) * scale);
+  const int bottom = (int)ceil(((double)rect->y + rect->h) * scale);
+
+  rect->x = left;
+  rect->y = top;
+  rect->w = right  - left;
+  rect->h = bottom - top;
+}
+
 inline static bool rectIntersects(const FrameDamageRect * r1,
     const FrameDamageRect * r2)
 {