Add fl_remove_scale()/fl_restore_scale() to transiently draw without scaling factor.

This new API is a response to this message in fltk.general :
Can custom box type functions handle their own high-DPI screen scaling?

2 files changed, 19 insertions, 0 deletions

diff --git a/src/drivers/Quartz/Fl_Quartz_Graphics_Driver.H b/src/drivers/Quartz/Fl_Quartz_Graphics_Driver.H
index b61761d6f..7e4aab962 100644
--- a/src/drivers/Quartz/Fl_Quartz_Graphics_Driver.H
+++ b/src/drivers/Quartz/Fl_Quartz_Graphics_Driver.H
@@ -188,6 +188,8 @@ protected:
   void descriptor_init(const char* name, Fl_Fontsize Size, Fl_Quartz_Font_Descriptor *d);
 #endif
   virtual void overlay_rect(int x, int y, int w , int h);
+  virtual float remove_scale();
+  virtual void restore_scale(float);
 };
 
 class Fl_Quartz_Printer_Graphics_Driver : public Fl_Quartz_Graphics_Driver {
diff --git a/src/drivers/Quartz/Fl_Quartz_Graphics_Driver.cxx b/src/drivers/Quartz/Fl_Quartz_Graphics_Driver.cxx
index 9d82d5c73..acabf6e73 100644
--- a/src/drivers/Quartz/Fl_Quartz_Graphics_Driver.cxx
+++ b/src/drivers/Quartz/Fl_Quartz_Graphics_Driver.cxx
@@ -17,6 +17,7 @@
 #include <config.h>
 #include "Fl_Quartz_Graphics_Driver.H"
 #include "../Darwin/Fl_Darwin_System_Driver.H"
+#include "../../Fl_Screen_Driver.H"
 #include <FL/platform.H>
 #include <FL/fl_draw.H>
 #include <FL/Fl_Image_Surface.H>
@@ -158,3 +159,19 @@ void Fl_Quartz_Graphics_Driver::cache_size(Fl_Image *img, int &width, int &heigh
   width *= 2 * scale();
   height *= 2 * scale();
 }
+
+float Fl_Quartz_Graphics_Driver::remove_scale() {
+  float s = scale();
+  if (s != 1.f && Fl_Display_Device::display_device()->is_current()) {
+    Fl::screen_driver()->scale(0, 1.f);
+    CGContextScaleCTM(gc_, 1/s, 1/s);
+  }
+  return s;
+}
+
+void Fl_Quartz_Graphics_Driver::restore_scale(float s) {
+  if (s != 1.f && Fl_Display_Device::display_device()->is_current()) {
+    Fl::screen_driver()->scale(0, s);
+    CGContextScaleCTM(gc_, s, s);
+  }
+}