shithub: sce

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grp: adjust alpha curve for better sprite rendition

scv engine glow looks slightly better this way

--- a/utils/grp.c

+++ b/utils/grp.c

@@ -106,9 +106,13 @@

 		switch(npal){

 		case 63:

 			if(i > 47)

-				a = (0xff + 1) / (1 + exp(-i + 48 - 3.4) / 0.75);

+				a = 0xff / (1 + exp(-i + 48 - 3.4) / 0.75);

+			/* logistic growth function

+			 * max / (1 + exp(-x + xofs) / slope) + yofs

+			 * fplot -r '0:47 0:255' '255 / (1 + exp((20 - x) / 4)) + 0'

+			 */

 			else

-				a = (0xff + 1) / (1 + exp(-i + 10.0) / 2.2);

+				a = (0xff + 1) / (1 + exp((16 - i) / 3.5)) + 0;

 			break;

 		/* FIXME */

 		case 40: a = i < 33 ? 0xff * i / 32 : 0xff * (6 - (i - 33)) / 6; break;