add alpha channel to sprites

README.md

@@ -43,7 +43,9 @@ For example, for apps running on a Mac/PC/Linux, it is usually set to `host`, wh
 
 If you are building for Nerves, it will use `cairo-fb`
 
+
 Previous versions of `scenic_driver_local` would use `bcm` (Broadcom Manager) for any of `rpi`, `rpi0`, `rip2`, `rpi3`, and `rpi3a` and `drm` for `bbb` and `rpi4`.
+
 You can explicitly use these by setting `SCENIC_LOCAL_TARGET=bcm` or `SCENIC_LOCAL_TARGET=drm`, **but these options are being deprecated**.
 Please try the default of `SCENIC_LOCAL_TARGET=cairo-fb` as this should work universally on any Nerves target.
 

c_src/device/cairo/cairo_script_ops.c

@@ -322,7 +322,8 @@ static void draw_sprite(scenic_cairo_ctx_t* p_ctx,
 
   cairo_rectangle(p_ctx->cr, sprite.dx, sprite.dy, sprite.dw, sprite.dh);
   cairo_scale(p_ctx->cr, sprite.dw / sprite.sw, sprite.dh / sprite.sh);
-  cairo_fill(p_ctx->cr);
+  cairo_clip(p_ctx->cr);
+  cairo_paint_with_alpha(p_ctx->cr, sprite.alpha);
 
   cairo_restore(p_ctx->cr);
 }

c_src/device/nvg/nvg_script_ops.c

@@ -223,7 +223,7 @@ void script_ops_draw_text(void* v_ctx,
 // see: https://github.com/memononen/nanovg/issues/348
 static void draw_image(NVGcontext* p_ctx,
                        sid_t id,
-                       const sprite_t s)
+                       const sprite_t sprite)
 {
   float ax, ay;
   NVGpaint img_pattern;
@@ -236,20 +236,20 @@ static void draw_image(NVGcontext* p_ctx,
   int iw,ih;
   nvgImageSize(p_ctx, p_image->image_id, &iw, &ih);
 
-  // Aspect ration of pixel in x an y dimensions. This allows us to scale
+  // Aspect ratio of pixel in x and y dimensions. This allows us to scale
   // the sprite to fill the whole rectangle.
-  ax = s.dw / s.sw;
-  ay = s.dh / s.sh;
+  ax = sprite.dw / sprite.sw;
+  ay = sprite.dh / sprite.sh;
 
   // create the temporary pattern
   img_pattern = nvgImagePattern(p_ctx,
-                                s.dx - s.sx*ax, s.dy - s.sy*ay,
+                                sprite.dx - sprite.sx*ax, sprite.dy - sprite.sy*ay,
                                 (float)iw*ax, (float)ih*ay,
-                                0, p_image->image_id, 1.0);
+                                0, p_image->image_id, sprite.alpha);
 
   // draw the image into a rect
   nvgBeginPath(p_ctx);
-  nvgRect(p_ctx, s.dx, s.dy, s.dw, s.dh);
+  nvgRect(p_ctx, sprite.dx, sprite.dy, sprite.dw, sprite.dh);
   nvgFillPaint(p_ctx, img_pattern);
   nvgFill(p_ctx);
 

c_src/scenic/script.c

@@ -317,10 +317,11 @@ void render_script(void* v_ctx, sid_t id)
               .dx = get_float(p, i + 16),
               .dy = get_float(p, i + 20),
               .dw = get_float(p, i + 24),
-              .dh = get_float(p, i + 28)
+              .dh = get_float(p, i + 28),
+              .alpha = get_float( p, i + 32 )
             };
 
-            i += 32;
+            i += 36;
           }
           script_ops_draw_sprites(v_ctx, id, count, sprites);
           free(sprites);

c_src/scenic/script_ops.c

@@ -222,10 +222,12 @@ void log_script_ops_draw_sprites(const char* prefix, const char* func, log_level
   for (int i = 0; i < count; i++) {
     log_message(level, "%s %s: index: %d %{"
                 "s: {{%.1f,%.1f},{%.1f,%.1f}}, "
-                "d: {{%.1f,%.1f},{%.1f,%.1f}}"
+                "d: {{%.1f,%.1f},{%.1f,%.1f}}, "
+                "alpha: %.1f}"
                 "}", prefix, func, i,
                 sprites[i].sx, sprites[i].sy, sprites[i].sw, sprites[i].sh,
-                sprites[i].dx, sprites[i].dy, sprites[i].dw, sprites[i].dh);
+                sprites[i].dx, sprites[i].dy, sprites[i].dw, sprites[i].dh,
+                sprites[i].alpha);
   }
 }
 

c_src/scenic/script_ops.h

@@ -76,6 +76,7 @@ typedef struct {
   float dy;
   float dw;
   float dh;
+  float alpha;
 } sprite_t;
 
 typedef struct {