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Doxygen: describe better support for OpenGL on HighDPI displays.

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ManoloFLTK
2019-04-12 18:47:42 +02:00
parent 4abaeba539
commit f55729ed32
4 changed files with 35 additions and 14 deletions
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documentation/src/opengl.dox
+21 -3
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@@ -25,9 +25,9 @@ the file \p <GL/gl.h> (on macOS: \p <OpenGL/gl.h>), define
some extra drawing functions provided by FLTK, and include the
\p <windows.h> header file needed by Windows applications.
Some simple coding rules (see \ref osissues_retina) allow to write
cross-platform code that will draw high resolution
OpenGL graphics if run on 'retina' displays with MacOS.
Some simple coding rules (see \ref opengl_highdpi) allow to write
cross-platform code that will support OpenGL run on HighDPI displays
(including the 'retina' displays of Apple hardware).
\section opengl_subclass Making a Subclass of Fl_Gl_Window
@@ -179,6 +179,24 @@ You must put <tt>glwindow->show()</tt> in your main code
after calling \p show() on the window containing the
OpenGL window.
\section opengl_highdpi OpenGL and support of HighDPI displays
HighDPI displays (including the so-called 'retina' displays of Apple
hardware) are supported by FLTK in such a way that 1 unit of an FLTK
quantity (say, the value given by Fl_Gl_Window::w()) corresponds to more
than 1 pixel on the display. Conversely, when a program specifies the width and height of the
OpenGL viewport, it is necessary to use an API that returns quantities expressed in pixels
as follows:
\code
Fl_Gl_Window *glw = ...;
glViewport(0, 0, glw->pixel_w(), glw->pixel_h());
\endcode
which makes use of the Fl_Gl_Window::pixel_w() and Fl_Gl_Window::pixel_h() functions giving
the size in pixels of an Fl_Gl_Window that is potentially mapped to a HighDPI display.
Method Fl_Gl_Window::pixels_per_unit() can also be useful in this context.
\note A further coding rule is necessary to properly support retina displays
and OpenGL under macOS (see \ref osissues_retina)
\section opengl_normal Using OpenGL in Normal FLTK Windows
You can put OpenGL code into the \p draw() method, as described in
documentation/src/osissues.dox
+2 -1
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@@ -857,7 +857,8 @@ the GL scene in pixels: if the Fl_Gl_Window is mapped on a retina display, these
reported by Fl_Widget::w() and Fl_Widget::h(); if it's mapped on a regular display, they return the same values
as w() and h(). These methods dynamically change their values if the window is moved into/out from a retina
display. If Fl::use_high_res_GL(1) is not called, all Fl_Gl_Window 's are drawn at low resolution.
These methods are synonyms of w() and h() on non-Mac OS X platforms, so the source code remains cross-platform.
These methods are useful on all platforms because Fl_Gl_Window::w() and Fl_Gl_Window::h() don't return,
on HighDPI displays, the quantitites in pixels necessary to OpenGL functions .
The Fl_Gl_Window::pixels_per_unit() method is useful when the OpenGL code depends on the pixel dimension
of the GL scene. This occurs, e.g., if a window's handle() method uses Fl::event_x() and Fl::event_y()