Introduce HiDPI + rescaling support for the X11 platform (+ partial support for WIN32)

Corresponds to STR #3320
1) HiDPI support consists in detecting the adequate scaling factor for the screen on which
FLTK maps a window, and scaling all FLTK units by this factor. FLTK tries to detect the correct
value of this factor at startup (see more details below). Environment variable
FLTK_SCALING_FACTOR can also be used to set this value.
2) Rescaling support consists in changing the scaling factor of all FLTK windows
in reply to ctrl/+/-/0/ keystrokes.

More details for the various platforms :

- X11: Support is very advanced. Some details need still to be improved.
Automatic detection of the correct starting value of the scaling factor works well
with the gnome desktop. The present code contains no support for this on
other desktops.  FLTK_SCALING_FACTOR provides a workaround.

-WIN32: Support is incomplete at this point, although many test
applications have partial or complete HiDPI and scaling support.
The current value of the system's scaling factor is correctly detected
at application startup. Apps respond to changes of this value in real time.
Support needs to define the FLTK_HIDPI_SUPPORT preprocessor variable
at compile time. This way, standard builds produce a code with the
default WIN32 HiDPI support, that is, where all graphics goes to an internal
buffer that gets enlarged by the system and then mapped to the HiDPI
display. To experiment with (or develop) the new HiDPI support requires
a modified build procedure in which  FLTK_HIDPI_SUPPORT is defined
at compile time. When the support will be complete, the requirement for the
definition of this preprocessor variable will be removed. The present commit
contains support for a single scaling factor. Eventually, per-screen scaling
factors should be implemented, as done for X11.

- MacOS: this commit does not give new HiDPI for this platform.
Eventually, window rescaling in reply to command/+/-/0/ is desirable.
Per-screen scaling factor makes no sense on this platform because
the OS itself takes care of the difference between the resolutions of
traditional and retina displays.


git-svn-id: file:///fltk/svn/fltk/branches/branch-1.4@12239 ea41ed52-d2ee-0310-a9c1-e6b18d33e121

1 files changed, 47 insertions, 4 deletions

diff --git a/src/drivers/Xlib/Fl_Xlib_Graphics_Driver.cxx b/src/drivers/Xlib/Fl_Xlib_Graphics_Driver.cxx
index 6d6cff681..741ceb89a 100644
--- a/src/drivers/Xlib/Fl_Xlib_Graphics_Driver.cxx
+++ b/src/drivers/Xlib/Fl_Xlib_Graphics_Driver.cxx
@@ -3,7 +3,7 @@
 //
 // Rectangle drawing routines for the Fast Light Tool Kit (FLTK).
 //
-// Copyright 1998-2016 by Bill Spitzak and others.
+// Copyright 1998-2017 by Bill Spitzak and others.
 //
 // This library is free software. Distribution and use rights are outlined in
 // the file "COPYING" which should have been included with this file.  If this
@@ -57,6 +57,7 @@ Fl_Xlib_Graphics_Driver::Fl_Xlib_Graphics_Driver(void) {
   p_size = 0;
   p = NULL;
   line_width_ = 0;
+  line_delta_ = 0;
 #if USE_PANGO
   pfd_ = pango_font_description_new();
   Fl_Graphics_Driver::font(0, 0);
@@ -78,8 +79,30 @@ void Fl_Xlib_Graphics_Driver::gc(void *value) {
   fl_gc = gc_;
 }
 
-void Fl_Xlib_Graphics_Driver::copy_offscreen(int x, int y, int w, int h, Fl_Offscreen pixmap, int srcx, int srcy) {
-  XCopyArea(fl_display, pixmap, fl_window, gc_, srcx, srcy, w, h, x+offset_x_, y+offset_y_);
+void Fl_Xlib_Graphics_Driver::scale(float f) {
+#if USE_XFT
+  if (f != scale_) {
+    size_ = 0;
+    scale_ = f;
+    //fprintf(stderr, "scale=%.2f\n", scale_);
+    line_style(FL_SOLID); // scale also default line width
+    /* Scaling >= 2 transforms 1-pixel wide lines into wider lines.
+     X11 draws 2-pixel wide lines so that half of the line width is above or at left
+     of a 1-pixel wide line that would be drawn with the same coordinates.
+     Thus, if the line starts at coordinates (0,0) half of the line width is invisible.
+     Similarly, if the line ends at w()-1 the last pixel of the window is not drawn.
+     What is wanted when scale_ == 2 is a visible 2-pixel wide line in the first case,
+     and a line at the window's edge in the 2nd case.
+     Setting line_delta_ to 1 and offsetting all line, rectangle, text and clip
+     coordinates by line_delta_ achieves what is wanted until scale_ <= 3.5.
+     */
+    line_delta_ =  (scale_ > 1.75 ? 1 : 0);
+  }
+#endif
+}
+
+void Fl_Xlib_Graphics_Driver::copy_offscreen_unscaled(float x, float y, float w, float h, Fl_Offscreen pixmap, float srcx, float srcy) {
+  XCopyArea(fl_display, pixmap, fl_window, gc_, srcx, srcy, w, h, x+offset_x_*scale_, y+offset_y_*scale_);
 }
 
 void Fl_Xlib_Graphics_Driver::add_rectangle_to_region(Fl_Region r, int X, int Y, int W, int H) {
@@ -88,7 +111,8 @@ void Fl_Xlib_Graphics_Driver::add_rectangle_to_region(Fl_Region r, int X, int Y,
   XUnionRectWithRegion(&R, r, r);
 }
 
-void Fl_Xlib_Graphics_Driver::transformed_vertex0(short x, short y) {
+void Fl_Xlib_Graphics_Driver::transformed_vertex0(float fx, float fy) {
+  short x = short(fx), y = short(fy);
   if (!n || x != p[n-1].x || y != p[n-1].y) {
     if (n >= p_size) {
       p_size = p ? 2*p_size : 16;
@@ -205,6 +229,25 @@ void Fl_Xlib_Graphics_Driver::font_name(int num, const char *name) {
   s->first = 0;
 }
 
+
+Region Fl_Xlib_Graphics_Driver::scale_clip(float f) {
+  Region r = rstack[rstackptr];
+  if (r == 0 || (f == 1 && offset_x_ == 0 && offset_y_ == 0) ) return 0;
+  float delta = (f >= 2 ? f/3 : 0);
+  Region r2 = XCreateRegion();
+  XRectangle R;
+  for (int i = 0; i < r->numRects; i++) {
+    R.x = short((r->rects[i].x1 + offset_x_)*f-delta + line_delta_);
+    R.y = short((r->rects[i].y1 + offset_y_)*f-delta + line_delta_);
+    R.width = short(r->rects[i].x2*f) - short(r->rects[i].x1*f);
+    R.height = short(r->rects[i].y2*f) - short(r->rects[i].y1*f);
+    XUnionRectWithRegion(&R, r2, r2);
+  }
+  rstack[rstackptr] = r2;
+  return r;
+}
+
+
 void Fl_Xlib_Graphics_Driver::translate_all(int dx, int dy) { // reversibly adds dx,dy to the offset between user and graphical coordinates
   stack_x_[depth_] = offset_x_;
   stack_y_[depth_] = offset_y_;