commit fdc09b028fde9d2ec70418735f354b51c8295d0f
author Weifeng Liu <weifeng.liu.z@gmail.com> Sun May 11 15:33:18 2025 +0800
committer Marc-André Lureau <marcandre.lureau@redhat.com> Sat May 24 17:04:00 2025 +0200
tree 59103a3b4b297e2c009c8f8a206174a4fcf2071c
parent a1b28f71f7ff0fcafbe0672b788e8e57ee4fe8f6

ui/gtk-gl-area: Render guest content with padding in fixed-scale mode

In fixed-scale mode (zoom-to-fit=false), we expect that scale should not
change, meaning that if window size is larger than guest surface,
padding is supposed to be added to preserve the scale. However, in
OpenGL mode (gl=on), guest surface is always painted to the whole canvas
without any padding. This change tries to fix this bug by adding
appropriate padding when drawing surfaces.

Signed-off-by: Weifeng Liu <weifeng.liu.z@gmail.com>
Message-ID: <20250511073337.876650-9-weifeng.liu.z@gmail.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Marc-André Lureau <marcandre.lureau@redhat.com>

ui/gtk-gl-area.c

diff --git a/ui/gtk-gl-area.c b/ui/gtk-gl-area.c
index db93cd6..8151cc4 100644
--- a/ui/gtk-gl-area.c
+++ b/ui/gtk-gl-area.c
@@ -44,7 +44,9 @@
 #endif
     int pw, ph, gs, y1, y2;
     int ww, wh;
+    int ww_surface, wh_surface;
     int fbw, fbh;
+    int wx_offset, wy_offset;
 
     if (!vc->gfx.gls) {
         return;
@@ -61,6 +63,17 @@
 
     gd_update_scale(vc, ww, wh, fbw, fbh);
 
+    ww_surface = fbw * vc->gfx.scale_x;
+    wh_surface = fbh * vc->gfx.scale_y;
+
+    wx_offset = wy_offset = 0;
+    if (ww > ww_surface) {
+        wx_offset = (ww - ww_surface) / 2;
+    }
+    if (wh > wh_surface) {
+        wy_offset = (wh - wh_surface) / 2;
+    }
+
     if (vc->gfx.scanout_mode) {
         if (!vc->gfx.guest_fb.framebuffer) {
             return;
@@ -79,11 +92,29 @@
         glBindFramebuffer(GL_READ_FRAMEBUFFER, vc->gfx.guest_fb.framebuffer);
         /* GtkGLArea sets GL_DRAW_FRAMEBUFFER for us */
 
+        if (wx_offset > 0) {
+            glEnable(GL_SCISSOR_TEST);
+            glScissor(0, 0, wx_offset * gs, wh * gs);
+            glClear(GL_COLOR_BUFFER_BIT);
+            glScissor((ww - wx_offset) * gs, 0, wx_offset * gs, wh * gs);
+            glClear(GL_COLOR_BUFFER_BIT);
+            glDisable(GL_SCISSOR_TEST);
+        }
+        if (wy_offset > 0) {
+            glEnable(GL_SCISSOR_TEST);
+            glScissor(0, 0, ww * gs, wy_offset * gs);
+            glClear(GL_COLOR_BUFFER_BIT);
+            glScissor(0, (wh - wy_offset) * gs, ww * gs, wy_offset * gs);
+            glClear(GL_COLOR_BUFFER_BIT);
+            glDisable(GL_SCISSOR_TEST);
+        }
+
         glViewport(0, 0, pw, ph);
         y1 = vc->gfx.y0_top ? 0 : vc->gfx.h;
         y2 = vc->gfx.y0_top ? vc->gfx.h : 0;
         glBlitFramebuffer(0, y1, vc->gfx.w, y2,
-                          0, 0, pw, ph,
+                          wx_offset * gs, wy_offset * gs,
+                          (ww - wx_offset) * gs, (wh - wy_offset) * gs,
                           GL_COLOR_BUFFER_BIT, GL_NEAREST);
 #ifdef CONFIG_GBM
         if (dmabuf) {