Merge pull request #735 from libgd/bug/661

fix #661, restore correct clamping, fixing alpha artifacts (these ones ar…

Author: pierrejoye

src/gd.c

@@ -3539,20 +3539,12 @@ BGD_DECLARE(void) gdImageCopyResampled (gdImagePtr dst,
 				green /= alpha_sum;
 				blue /= alpha_sum;
 			}
-			/* Clamping to allow for rounding errors above */
-			if (red > 255.0) {
-				red = 255.0;
-			}
-			if (green > 255.0) {
-				green = 255.0;
-			}
-			if (blue > 255.0f) {
-				blue = 255.0;
-			}
-			if (alpha > gdAlphaMax) {
-				alpha = gdAlphaMax;
-			}
-			gdImageSetPixel(dst, x, y, gdTrueColorAlpha ((int) red, (int) green, (int) blue, (int) alpha));
+			/* Round up closest next channel value and clamp to max channel value */
+			red = red >= 255.5 ? 255 : red+0.5;
+			blue = blue >= 255.5 ? 255 : blue+0.5;
+			green = green >= 255.5 ? 255 : green+0.5;
+			alpha = alpha >= gdAlphaMax+0.5 ? 255 : alpha+0.5;
+			gdImageSetPixel(dst, x, y, gdTrueColorAlpha ((int)red, (int)green, (int)blue, (int)alpha));
 		}
 	}
 }