Merge pull request #1438 from floooh/issue1437/ios_pass_dimensions

sokol_app.h ios/mtl: Fix drawable size mismatch assert on rotate 

2 files changed, 37 insertions, 8 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 02789ce3..ec7486c7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,22 @@
 ## Updates
 
+### 08-Feb-2026
+
+- sokol_app.h ios/mtl: Fix a spurious assert when applying scissor rect after
+  rotating the device and which might lead to a drawable-size mismatch. This
+  doesn't appear to be 100% watertight but works much better than
+  before. The assert might be the result of a behaviour change in MTKView
+  between iOS versions (which tbh wouldn't be the first time this happened).
+  A 'perfect' solution will need to wait until the next round of iOS/macOS
+  window system glue updates which will finally get rid of MTKView and instead
+  use `CAMetalLayer` and `CADisplayLink` directly. Until then it's definitely
+  recommended to disable display rotation for your application via the Info.plist
+  file. Many thanks to @ArMuSebastian for writing the issue and providing
+  a simple reproducer.
+
+  Issue: https://github.com/floooh/sokol/issues/1437
+  PR: https://github.com/floooh/sokol/pull/1438
+
 ### 03-Feb-2026
 
 - sokol_gfx.h vulkan: another round of small fixes and code cleanups in the
diff --git a/sokol_app.h b/sokol_app.h
index 7fa97330..3b965980 100644
--- a/sokol_app.h
+++ b/sokol_app.h
@@ -6215,16 +6215,23 @@ _SOKOL_PRIVATE void _sapp_ios_mtl_discard_state(void) {
 }
 
 _SOKOL_PRIVATE bool _sapp_ios_mtl_update_framebuffer_dimensions(CGRect screen_rect) {
-    _sapp.framebuffer_width = _sapp_roundf_gzero(screen_rect.size.width * _sapp.dpi_scale);
-    _sapp.framebuffer_height = _sapp_roundf_gzero(screen_rect.size.height * _sapp.dpi_scale);
-    const CGSize fb_size = _sapp.ios.view.drawableSize;
-    int cur_fb_width = _sapp_roundf_gzero(fb_size.width);
-    int cur_fb_height = _sapp_roundf_gzero(fb_size.height);
-    bool dim_changed = (_sapp.framebuffer_width != cur_fb_width) || (_sapp.framebuffer_height != cur_fb_height);
-    if (dim_changed) {
-        const CGSize drawable_size = { (CGFloat) _sapp.framebuffer_width, (CGFloat) _sapp.framebuffer_height };
+    // get current screen size and if it changed, update the MTKView drawable size
+    const int screen_width = _sapp_roundf_gzero(screen_rect.size.width * _sapp.dpi_scale);
+    const int screen_height = _sapp_roundf_gzero(screen_rect.size.height * _sapp.dpi_scale);
+    const CGSize view_size = _sapp.ios.view.drawableSize;
+    const int view_width = _sapp_roundf_gzero(view_size.width);
+    const int view_height = _sapp_roundf_gzero(view_size.height);
+    const bool needs_update = (screen_width != view_width) || (screen_height != view_height);
+    if (needs_update) {
+        const CGSize drawable_size = { (CGFloat) screen_width, (CGFloat) screen_height };
         _sapp.ios.view.drawableSize = drawable_size;
     }
+    // now separately, get the current drawable's size
+    const int cur_fb_width = _sapp_roundf_gzero(_sapp.ios.view.currentDrawable.texture.width);
+    const int cur_fb_height = _sapp_roundf_gzero(_sapp.ios.view.currentDrawable.texture.height);
+    const bool dim_changed = (cur_fb_width != _sapp.framebuffer_width) || (cur_fb_height != _sapp.framebuffer_height);
+    _sapp.framebuffer_width = cur_fb_width;
+    _sapp.framebuffer_height = cur_fb_height;
     return dim_changed;
 }
 #endif
@@ -6366,6 +6373,11 @@ _SOKOL_PRIVATE void _sapp_ios_update_dimensions(void) {
 }
 
 _SOKOL_PRIVATE void _sapp_ios_frame(void) {
+    // NOTE: it's not great to call _sapp_ios_update_dimensions() so early in
+    // the frame, since this calls MTKView.currentDrawable, which should be
+    // delayed until the latest possible moment (e.g. sapp_get_swapchain()).
+    // MTKView is on the chopping block anyway though, so don't bother too much
+    // getting it right until MTKView is replaced with CAMetalLayer.
     _sapp_ios_update_dimensions();
     _sapp_frame();
 }