Improve X11 coordinate clipping for text (STR 2798)

Text outside the 16-bit X11 coordinate space must be clipped before
calling X11 draw functions, otherwise text might appear anywhere
in the window because X11 would "truncate" the coordinates instead
of proper clipping (X11 handles only 16-bit coordinates).

CHANGES.txt

@@ -111,6 +111,9 @@ Changes in FLTK 1.4.0					Released: ??? ?? 2019
   Other Improvements
 
   - (add new items here)
+  - Improve X11 16-bit coordinate clipping for text (STR 2798). This
+    assumes that text is "small" WRT 16-bit coordinate space and clips
+    text if at least one of the x/y coordinates is out of bounds.
   - Fix Fl::add_timeout() in draw() under Linux (STR 3188)
   - Class Fl_Native_File_Chooser uses in priority the file chooser dialog
     of GTK version 3 when available on the running X11 platform, and falls back

src/drivers/Xlib/Fl_Xlib_Graphics_Driver_font_x.cxx

@@ -642,23 +642,33 @@ void Fl_Xlib_Graphics_Driver::text_extents_unscaled(const char *c, int n, int &d
   if (gc_) XUtf8_measure_extents(fl_display, fl_window, ((Fl_Xlib_Font_Descriptor*)font_descriptor())->font, gc_, &xx, &yy, &ww, &hh, c, n);
 
   W = ww; H = hh; dx = xx; dy = yy;
-// This is the safe but mostly wrong thing we used to do...
-//  W = 0; H = 0;
-//  fl_measure(c, W, H, 0);
-//  dx = 0;
-//  dy = fl_descent() - H;
 }
 
 void Fl_Xlib_Graphics_Driver::draw_unscaled(const char* c, int n, int x, int y) {
+
+  // transform coordinates and clip if outside 16-bit space (STR 2798)
+
+  int x1 = x + offset_x_;
+  if (x1 < clip_min() || x1 > clip_max()) return;
+
+  int y1 = y + offset_y_;
+  if (y1 < clip_min() || y1 > clip_max()) return;
+
   if (font_gc != gc_) {
     if (!font_descriptor()) this->font(FL_HELVETICA, FL_NORMAL_SIZE);
     font_gc = gc_;
     XSetFont(fl_display, gc_, ((Fl_Xlib_Font_Descriptor*)font_descriptor())->font->fid);
   }
-  if (gc_) XUtf8DrawString(fl_display, fl_window, ((Fl_Xlib_Font_Descriptor*)font_descriptor())->font, gc_, x+offset_x_, y+offset_y_, c, n);
+  if (gc_) XUtf8DrawString(fl_display, fl_window, ((Fl_Xlib_Font_Descriptor*)font_descriptor())->font, gc_, x1, y1, c, n);
 }
 
 void Fl_Xlib_Graphics_Driver::draw_unscaled(int angle, const char *str, int n, int x, int y) {
+
+  // clip if outside 16-bit space (STR 2798)
+
+  if (x < clip_min() || x > clip_max()) return;
+  if (y < clip_min() || y > clip_max()) return;
+
   static char warning = 0; // issue warning only once
   if (!warning && angle != 0) {
     warning = 1;
@@ -670,11 +680,20 @@ void Fl_Xlib_Graphics_Driver::draw_unscaled(int angle, const char *str, int n, i
 }
 
 void Fl_Xlib_Graphics_Driver::rtl_draw_unscaled(const char* c, int n, int x, int y) {
+
+  // transform coordinates and clip if outside 16-bit space (STR 2798)
+
+  int x1 = x + offset_x_;
+  if (x1 < clip_min() || x1 > clip_max()) return;
+
+  int y1 = y + offset_y_;
+  if (y1 < clip_min() || y1 > clip_max()) return;
+
   if (font_gc != gc_) {
     if (!font_descriptor()) this->font(FL_HELVETICA, FL_NORMAL_SIZE);
     font_gc = gc_;
   }
-  if (gc_) XUtf8DrawRtlString(fl_display, fl_window, ((Fl_Xlib_Font_Descriptor*)font_descriptor())->font, gc_, x+offset_x_, y+offset_y_, c, n);
+  if (gc_) XUtf8DrawRtlString(fl_display, fl_window, ((Fl_Xlib_Font_Descriptor*)font_descriptor())->font, gc_, x1, y1, c, n);
 }
 
 float Fl_Xlib_Graphics_Driver::scale_font_for_PostScript(Fl_Font_Descriptor *desc, int s) {

src/drivers/Xlib/Fl_Xlib_Graphics_Driver_font_xft.cxx

@@ -782,6 +782,15 @@ void Fl_Xlib_Graphics_Driver::text_extents_unscaled(const char *c, int n, int &d
 }
 
 void Fl_Xlib_Graphics_Driver::draw_unscaled(const char *str, int n, int x, int y) {
+
+  // transform coordinates and clip if outside 16-bit space (STR 2798)
+
+  int x1 = x + offset_x_ * scale() + line_delta_;
+  if (x1 < clip_min() || x1 > clip_max()) return;
+
+  int y1 = y + offset_y_ * scale() + line_delta_;
+  if (y1 < clip_min() || y1 > clip_max()) return;
+
 #if USE_OVERLAY
   XftDraw*& draw_ = fl_overlay ? draw_overlay : ::draw_;
   if (fl_overlay) {
@@ -814,9 +823,9 @@ void Fl_Xlib_Graphics_Driver::draw_unscaled(const char *str, int n, int x, int y
     
     const wchar_t *buffer = utf8reformat(str, n);
 #ifdef __CYGWIN__
-    XftDrawString16(draw_, &color, ((Fl_Xlib_Font_Descriptor*)font_descriptor())->font, x+offset_x_*scale()+line_delta_, y+offset_y_*scale()+line_delta_, (XftChar16 *)buffer, n);
+    XftDrawString16(draw_, &color, ((Fl_Xlib_Font_Descriptor*)font_descriptor())->font, x1, y1, (XftChar16 *)buffer, n);
 #else
-    XftDrawString32(draw_, &color, ((Fl_Xlib_Font_Descriptor*)font_descriptor())->font, x+offset_x_*scale()+line_delta_, y+offset_y_*scale()+line_delta_, (XftChar32 *)buffer, n);
+    XftDrawString32(draw_, &color, ((Fl_Xlib_Font_Descriptor*)font_descriptor())->font, x1, y1, (XftChar32 *)buffer, n);
 #endif
   }
 }