Fix egd_render transparent to use float constants

The render engine has float guards to enhance beam code
generation. However, the default case used integers which
caused the engine to crash.

This is now fixed.

lib/percept/src/egd_render.erl

@@ -179,7 +179,7 @@ color(Trans,Layers,Type,OldC) ->
 
 color([],_) -> {0.0,0.0,0.0,0.0};
 color([{_,C}|_],opaque) -> C;    
-color(Layers,alpha) -> color1({0,0,0,0},Layers).
+color(Layers,alpha) -> color1({0.0,0.0,0.0,0.0},Layers).
 
 color1(Color,[]) -> Color;
 color1(Color,[{_,C}|Layers]) -> color1(alpha_blend(Color,C),Layers).

lib/percept/test/egd_SUITE.erl

@@ -143,6 +143,8 @@ image_shape(Config) when is_list(Config) ->
     ?line ok = bitmap_point_has_color(Bitmap, {W,H}, Pt2, Fgc),
     ?line ok = bitmap_point_has_color(Bitmap, {W,H}, Pt1, Fgc),
 
+    ?line <<_/binary>> = egd:render(Im, raw_bitmap, [{render_engine, alpha}]),
+
     ?line ok = egd:destroy(Im),
     erase(image_size),
     ok.
@@ -177,6 +179,8 @@ image_primitives(Config) when is_list(Config) ->
     ?line ok = bitmap_point_has_color(Bitmap, {W,H}, Pt2, Fgc),
     ?line ok = bitmap_point_has_color(Bitmap, {W,H}, Pt1, Fgc),
 
+    ?line <<_/binary>> = egd_render:binary(Im2, alpha),
+
     erase(image_size),
     ok.