Make Fl::set_color(r,g,b,a) effective under Wayland and macOS.

src/Fl_Graphics_Driver.cxx

@@ -45,6 +45,7 @@ Fl_Graphics_Driver::Fl_Graphics_Driver()
 {
   font_ = 0;
   size_ = 0;
+  color_ = FL_BLACK;
   sptr=0; rstackptr=0;
   rstack[0] = NULL;
   fl_clip_state_number=0;

src/Fl_cocoa.mm

@@ -2239,6 +2239,8 @@ static FLTextInputContext* fltextinputcontext_instance = nil;
                                        CGBitmapContextGetBitsPerComponent(gc), CGBitmapContextGetBytesPerRow(gc),
                                        CGBitmapContextGetColorSpace(gc), CGBitmapContextGetBitmapInfo(gc));
   }
+  CGContextClearRect(aux_bitmap, CGRectMake(0, 0,
+                     CGBitmapContextGetWidth(aux_bitmap), CGBitmapContextGetHeight(aux_bitmap)));
   if (r) CGContextScaleCTM(aux_bitmap, 2, 2);
 }
 - (void)reset_aux_bitmap {

src/drivers/Cairo/Fl_Cairo_Graphics_Driver.cxx

@@ -31,6 +31,7 @@
 #include <stdlib.h>  // abs(int)
 #include <string.h>  // memcpy()
 
+extern unsigned fl_cmap[256]; // defined in fl_color.cxx
 
 // duplicated from Fl_PostScript.cxx
 struct callback_data {
@@ -331,9 +332,29 @@ void Fl_Cairo_Graphics_Driver::color(unsigned char r, unsigned char g, unsigned
   check_status();
 }
 
-void Fl_Cairo_Graphics_Driver::color(Fl_Color c) {
-  Fl::get_color(c, cr_, cg_, cb_);
-  Fl_Cairo_Graphics_Driver::color(cr_, cg_, cb_);
+void Fl_Cairo_Graphics_Driver::color(Fl_Color i) {
+  Fl_Graphics_Driver::color(i);
+  if (!cairo_) return; // no context yet? We will assign the color later.
+  uchar r, g, b;
+  double fa = 1.0;
+  if (i & 0xFFFFFF00) {
+    // translate rgb colors into color index
+    r = i>>24;
+    g = i>>16;
+    b = i>> 8;
+  } else {
+    // translate index into rgb:
+    unsigned c = fl_cmap[i];
+    c = c ^ 0x000000ff; // trick to restore the color's correct alpha value
+    r = c>>24;
+    g = c>>16;
+    b = c>> 8;
+    fa = (c & 0xff)/255.0;
+  }
+  double fr = r/255.0;
+  double fg = g/255.0;
+  double fb = b/255.0;
+  cairo_set_source_rgba(cairo_, fr, fg, fb, fa);
 }
 
 Fl_Color Fl_Cairo_Graphics_Driver::color() { return Fl_Graphics_Driver::color(); }

src/drivers/Quartz/Fl_Quartz_Graphics_Driver_color.cxx

@@ -34,6 +34,7 @@ extern unsigned fl_cmap[256]; // defined in fl_color.cxx
 void Fl_Quartz_Graphics_Driver::color(Fl_Color i) {
   Fl_Graphics_Driver::color(i);
   uchar r, g, b;
+  float fa = 1.0f;
   if (i & 0xFFFFFF00) {
     // translate rgb colors into color index
     r = i>>24;
@@ -42,16 +43,20 @@ void Fl_Quartz_Graphics_Driver::color(Fl_Color i) {
   } else {
     // translate index into rgb:
     unsigned c = fl_cmap[i];
+    c = c ^ 0x000000ff; // trick to restore the color's correct alpha value
     r = c>>24;
     g = c>>16;
     b = c>> 8;
+    uchar a = c & 0xff;
+    //printf("i=%d rgb=%u,%u,%u a=%u\n",i,r,g,b,a);
+    fa = a/255.0f;
   }
   if (!gc_) return; // no context yet? We will assign the color later.
   float fr = r/255.0f;
   float fg = g/255.0f;
   float fb = b/255.0f;
-  CGContextSetRGBFillColor(gc_, fr, fg, fb, 1.0f);
-  CGContextSetRGBStrokeColor(gc_, fr, fg, fb, 1.0f);
+  CGContextSetRGBFillColor(gc_, fr, fg, fb, fa);
+  CGContextSetRGBStrokeColor(gc_, fr, fg, fb, fa);
 }
 
 void Fl_Quartz_Graphics_Driver::color(uchar r, uchar g, uchar b) {

src/fl_color.cxx

@@ -68,6 +68,8 @@ void Fl::set_color(Fl_Color i, uchar red, uchar green, uchar blue) {
  Sets an entry in the fl_color index table.
 
  You can set it to any 8-bit RGBA color.
+ \note The color transparency is effective under the Wayland, hybrid Wayland/X11 and macOS platforms, whereas it has no effect under the X11 and Windows platforms. It's also effective for widgets added to an Fl_Gl_Window.
+ \version 1.4
  */
 void Fl::set_color(Fl_Color i, uchar red, uchar green, uchar blue, uchar alpha) {
   Fl::set_color((Fl_Color)(i & 255),