Fix fl_read_image() under MacOS platform when GUI is rescaled.

This commit also simplifies the platform-dependent support of fl_read_image():
only Fl_XXX_Screen_Driver::read_win_rectangle() contains platform-specific
code to capture pixels from the current window or from an offscreen buffer.
Platform-independent function Fl_Screen_Driver::traverse_to_gl_subwindows()
captures subwindows that intersect with the area fl_read_image() targets.

git-svn-id: file:///fltk/svn/fltk/branches/branch-1.4@12653 ea41ed52-d2ee-0310-a9c1-e6b18d33e121

2 files changed, 26 insertions, 0 deletions

diff --git a/src/drivers/Quartz/Fl_Quartz_Graphics_Driver.H b/src/drivers/Quartz/Fl_Quartz_Graphics_Driver.H
index 60a261e94..b23817d46 100644
--- a/src/drivers/Quartz/Fl_Quartz_Graphics_Driver.H
+++ b/src/drivers/Quartz/Fl_Quartz_Graphics_Driver.H
@@ -184,6 +184,8 @@ protected:
 #else
   void descriptor_init(const char* name, Fl_Fontsize Size, Fl_Quartz_Font_Descriptor *d);
 #endif
+  virtual bool overlay_rect_unscaled() {return false; }
+  virtual void overlay_rect(int x, int y, int w , int h);
 };
 
 class Fl_Quartz_Printer_Graphics_Driver : public Fl_Quartz_Graphics_Driver {
diff --git a/src/drivers/Quartz/Fl_Quartz_Graphics_Driver_rect.cxx b/src/drivers/Quartz/Fl_Quartz_Graphics_Driver_rect.cxx
index 3a83b94d6..8153f4e78 100644
--- a/src/drivers/Quartz/Fl_Quartz_Graphics_Driver_rect.cxx
+++ b/src/drivers/Quartz/Fl_Quartz_Graphics_Driver_rect.cxx
@@ -173,6 +173,30 @@ void Fl_Quartz_Graphics_Driver::loop(int x, int y, int x1, int y1, int x2, int y
   if (quartz_line_width_ > 1.5f) CGContextSetShouldAntialias(gc_, false);
 }
 
+// returns y of horizontal line corresponding to pixels of current window
+// read by Fl_Cocoa_Screen_Driver::read_win_rectangle(  -,  y, -, 1)
+// when GUI is scaled by s
+static float overlay_y(int y, float s, int H) {
+  int a, b, c;
+  a = int(H*s) - (y+1)*s; // in Cocoa units from window bottom
+  c = (s > 1 ? s : 1); // height of pixels read in Cocoa units
+  b = H*s - (a+c); // top of read image from window top in Cocoa units
+  return b/s; // top of read image from window top in FLTK units
+}
+
+void Fl_Quartz_Graphics_Driver::overlay_rect(int x, int y, int w , int h) {
+  float s = scale();
+  CGContextSetLineWidth(gc_, 0.01);
+  int H = Fl_Window::current()->h();
+  CGContextMoveToPoint(gc_, x, overlay_y(y, s, H));
+  CGContextAddLineToPoint(gc_, x+w-1, overlay_y(y, s, H));
+  CGContextAddLineToPoint(gc_, x+w-1, overlay_y(y+h-1, s, H));
+  CGContextAddLineToPoint(gc_, x, overlay_y(y+h-1, s, H));
+  CGContextClosePath(gc_);
+  CGContextStrokePath(gc_);
+  CGContextSetLineWidth(gc_, quartz_line_width_);
+}
+
 void Fl_Quartz_Graphics_Driver::polygon(int x, int y, int x1, int y1, int x2, int y2) {
   CGContextSetShouldAntialias(gc_, true);
   CGContextMoveToPoint(gc_, x, y);