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