WIP: testing usage of SDL renderer

It does segfault.
2021-04-23 11:58:53 +02:00
parent 9d9c7f291c
commit 685b8c82d0
3 changed files with 164 additions and 5 deletions
@@ -0,0 +1,97 @@
+## Window creation for Retina displays
+
+The file info.plist sets NSHighResolutionCapable to true. This is fine for High-DPI
+and retina displays.
+
+The `SDL_CreateWindow` is called with the flag `SDL_WINDOW_ALLOW_HIGHDPI`.
+On Mac OS it means that, in source file `video/cocoa/SDL_cocoawindow.m`, from
+function `Cocoa_CreateWindow`, SDL calls:
+
+```objc
+/* highdpi will be TRUE below */
+BOOL highdpi = (window->flags & SDL_WINDOW_ALLOW_HIGHDPI) != 0;
+[contentView setWantsBestResolutionOpenGLSurface:highdpi]
+```
+
+Documentation for `setWantsBestResolutionOpenGLSurface`:
+
+https://developer.apple.com/documentation/appkit/nsview/1414938-wantsbestresolutionopenglsurface
+
+with more details in "OpenGL Programming Guide for Mac", chapter
+"Optimizing OpenGL for High Resolution":
+
+https://developer.apple.com/library/archive/documentation/GraphicsImaging/Conceptual/OpenGL-MacProgGuide/EnablingOpenGLforHighResolution/EnablingOpenGLforHighResolution.html#//apple_ref/doc/uid/TP40001987-CH1001-SW4
+
+Citation from the official documentation:
+
+You can opt in to high resolution by calling the method
+`setWantsBestResolutionOpenGLSurface:` when you initialize the view, and
+supplying YES as an argument:
+
+```objc
+[self  setWantsBestResolutionOpenGLSurface:YES];
+```
+
+If you don’t opt in, the system magnifies the rendered results.
+
+The wantsBestResolutionOpenGLSurface property is relevant only for views to
+which an NSOpenGLContext object is bound. Its value does not affect the behavior
+of other views. For compatibility, wantsBestResolutionOpenGLSurface defaults to
+NO, providing a 1-pixel-per-point framebuffer regardless of the backing scale
+factor for the display the view occupies. Setting this property to YES for a
+given view causes AppKit to allocate a higher-resolution framebuffer when
+appropriate for the backing scale factor and target display.
+
+To function correctly with wantsBestResolutionOpenGLSurface set to YES, a view
+must perform correct conversions between view units (points) and pixel units as
+needed. For example, the common practice of passing the width and height of
+[self bounds] to glViewport() will yield incorrect results at high resolution,
+because the parameters passed to the glViewport() function must be in pixels. As
+a result, you’ll get only partial instead of complete coverage of the render
+surface. Instead, use the backing store bounds:
+
+```objc
+[self convertRectToBacking:[self bounds]];
+```
+
+## Coordinates
+
+The SDL function `SDL_GL_GetDrawableSize` will provide the size of the underlying drawable
+in pixels. From the `SDL_video.h` header.
+
+```c
+/**
+ *  \brief Get the size of a window's underlying drawable in pixels (for use
+ *         with glViewport).
+ *
+ *  \param window   Window from which the drawable size should be queried
+ *  \param w        Pointer to variable for storing the width in pixels, may be NULL
+ *  \param h        Pointer to variable for storing the height in pixels, may be NULL
+ *
+ * This may differ from SDL_GetWindowSize() if we're rendering to a high-DPI
+ * drawable, i.e. the window was created with SDL_WINDOW_ALLOW_HIGHDPI on a
+ * platform with high-DPI support (Apple calls this "Retina"), and not disabled
+ * by the SDL_HINT_VIDEO_HIGHDPI_DISABLED hint.
+ *
+ *  \sa SDL_GetWindowSize()
+ *  \sa SDL_CreateWindow()
+ */
+extern DECLSPEC void SDLCALL SDL_GL_GetDrawableSize(SDL_Window * window, int *w,
+                                                    int *h);
+```
+
+In turns it calls `Cocoa_GL_GetDrawableSize` from source file
+`video/cocoa/SDL_cocoaopengl.m`. The function use the method
+`[contentView convertRectToBacking:viewport]`:
+
+```objc
+    if (window->flags & SDL_WINDOW_ALLOW_HIGHDPI) {
+        /* This gives us the correct viewport for a Retina-enabled view, only
+         * supported on 10.7+. */
+        if ([contentView respondsToSelector:@selector(convertRectToBacking:)]) {
+            viewport = [contentView convertRectToBacking:viewport];
+        }
+    }
+```
+
+to give back the sizes in pixels.