Fix color2int, int2color alpha handling (libgd alpha is 0-127)

Martijn Versteegh · sfan5 · commit f7b0d5c5327a · 2018-11-22T21:05:13.000+01:00
diff --git a/Image.cpp b/Image.cpp
@@ -19,7 +19,7 @@
 
 static inline int color2int(Color c)
 {
-	u8 a = 255 - c.a;
+	u8 a = (255 - c.a) * gdAlphaMax / 255;
 	return (a << 24) | (c.r << 16) | (c.g << 8) | c.b;
 }
 
@@ -31,7 +31,7 @@ static inline Color int2color(int c)
 	c2.g = (c >> 8) & 0xff;
 	c2.r = (c >> 16) & 0xff;
 	a = (c >> 24) & 0xff;
-	c2.a = 255 - a;
+	c2.a = 255 - (a*255 / gdAlphaMax);
 	return c2;
 }
 

Original file line number	Diff line number	Diff line change
`@@ -19,7 +19,7 @@`
`19`	`19`
`20`	`20`	`static inline int color2int(Color c)`
`21`	`21`	`{`
`22`		`- u8 a = 255 - c.a;`
	`22`	`+ u8 a = (255 - c.a) * gdAlphaMax / 255;`
`23`	`23`	`return (a << 24) \| (c.r << 16) \| (c.g << 8) \| c.b;`
`24`	`24`	`}`
`25`	`25`
`@@ -31,7 +31,7 @@ static inline Color int2color(int c)`
`31`	`31`	`c2.g = (c >> 8) & 0xff;`
`32`	`32`	`c2.r = (c >> 16) & 0xff;`
`33`	`33`	`a = (c >> 24) & 0xff;`
`34`		`- c2.a = 255 - a;`
	`34`	`+ c2.a = 255 - (a*255 / gdAlphaMax);`
`35`	`35`	`return c2;`
`36`	`36`	`}`
`37`	`37`