Correct the drawing surface density on non-HiDPI displays (macOS)

CMakeLists.txt

@@ -80,6 +80,7 @@ set (SIMPLEGRAPHIC_PLATFORM_SOURCES)
 if (APPLE)
     set (SIMPLEGRAPHIC_PLATFORM_SOURCES
         "engine/system/win/sys_macos.mm"
+        "engine/system/win/sys_platform_macos.h"
     )
 endif()
 

engine/render/r_main.cpp

@@ -1164,6 +1164,7 @@ void r_renderer_c::BeginFrame()
 	ImGui_ImplGlfw_NewFrame();
 	ImGui::NewFrame();
 	{
+		sys->video->SyncSurfaceScale();
 		auto& vid = sys->video->vid;
 		int wNew = VirtualScreenWidth();
 		int hNew = VirtualScreenHeight();

engine/system/sys_video.h

@@ -50,6 +50,7 @@ class sys_IVideo {
 	virtual void	SetForeground() = 0; // Activate the window if shown
 	virtual bool	IsActive() = 0; // Get activated status
 	virtual void	FramebufferSizeChanged(int width, int height) = 0; // Respond to framebuffer size change
+	virtual void	SyncSurfaceScale() = 0; // Keep the drawing surface density matched to the display
 	virtual void	SizeChanged(int width, int height, bool max) = 0; // Respond to window size change
 	virtual void	PosChanged(int x, int y) = 0; // Respond to window position change
 	virtual void	GetMinSize(int &width, int &height) = 0; // Get minimum window size

engine/system/win/sys_macos.mm

@@ -1,6 +1,13 @@
 #include <string_view>
 #include <CoreFoundation/CFBundle.h>
 #include <ApplicationServices/ApplicationServices.h>
+#include <Cocoa/Cocoa.h>
+
+#define GLFW_EXPOSE_NATIVE_COCOA
+#include <GLFW/glfw3.h>
+#include <GLFW/glfw3native.h>
+
+#include "sys_platform_macos.h"
 
 const char* PlatformOpenURL(const char* textUrl)
 {
@@ -10,3 +17,29 @@
     CFRelease(url);
     return nullptr;
 }
+
+bool Platform_SyncLayerScale(GLFWwindow* window)
+{
+    // The layer the renderer draws into can be left at a pixel density that
+    // doesn't match the display the window is on, which makes the drawing
+    // surface larger than the size the window system reports. Everything then
+    // renders into a fraction of the window.
+    NSWindow* w = glfwGetCocoaWindow(window);
+    if (!w) {
+        return false;
+    }
+    NSView* v = [w contentView];
+    CALayer* layer = [v layer];
+    if (!layer) {
+        return false;
+    }
+    CGFloat want = [w backingScaleFactor];
+    if (want <= 0.0 || fabs([layer contentsScale] - want) < 0.01) {
+        return false;
+    }
+    [layer setContentsScale:want];
+    for (CALayer* sub in [layer sublayers]) {
+        [sub setContentsScale:want];
+    }
+    return true;
+}

engine/system/win/sys_platform_macos.h

@@ -0,0 +1,12 @@
+// SimpleGraphic Engine
+//
+// macOS platform helpers
+//
+
+#pragma once
+
+struct GLFWwindow;
+
+// Keep the layer being rendered into at the same pixel density as the display
+// the window is on. Returns true when it had to be corrected.
+bool Platform_SyncLayerScale(GLFWwindow* window);

engine/system/win/sys_video.cpp

@@ -8,6 +8,9 @@
 #include <glad/gles2.h>
 
 #include "sys_local.h"
+#ifdef __APPLE__
+#include "sys_platform_macos.h"
+#endif
 #include "core.h"
 
 #include <GLFW/glfw3.h>
@@ -32,6 +35,7 @@ class sys_video_c : public sys_IVideo {
 	void	SetForeground();
 	bool	IsActive();
 	void	FramebufferSizeChanged(int width, int height);
+	void	SyncSurfaceScale();
 	void	SizeChanged(int width, int height, bool max);
 	void	PosChanged(int x, int y);
 	void	GetMinSize(int& width, int& height);
@@ -677,6 +681,25 @@ void sys_video_c::FramebufferSizeChanged(int width, int height)
 	}
 }
 
+void sys_video_c::SyncSurfaceScale()
+{
+#ifdef __APPLE__
+	if (!wnd) {
+		return;
+	}
+	if (Platform_SyncLayerScale(wnd)) {
+		// The surface was rebuilt at the correct density; re-read the size
+		// that describes it.
+		int fbW = 0, fbH = 0;
+		glfwGetFramebufferSize(wnd, &fbW, &fbH);
+		if (fbW > 0 && fbH > 0) {
+			vid.fbSize[0] = fbW;
+			vid.fbSize[1] = fbH;
+		}
+	}
+#endif
+}
+
 void sys_video_c::SizeChanged(int width, int height, bool max)
 {
 	// Avoid persisting an invalid window size from being minimized.