# HG changeset patch
# User Michael Pavone <pavone@retrodev.com>
# Date 1483262203 28800
# Node ID fd3b8ac57aca6e4fcf8d88d1f22c6c62c31a90aa
# Parent  136b1676109bcc121240f51aa5e0afdc70c849c3
Fix rendering of BG color index 0 in Mode 4. Only transparent with respect to sprites and not the backdrop like in Mode 5

diff -r 136b1676109b -r fd3b8ac57aca vdp.c
--- a/vdp.c	Sun Jan 01 01:10:44 2017 -0800
+++ b/vdp.c	Sun Jan 01 01:16:43 2017 -0800
@@ -1260,32 +1260,19 @@
 			for (int i = 0; i < 8; i++, sprite_src++)
 			{
 				uint8_t *bg_src = context->tmp_buf_a + ((8 + i + col * 8 - (context->hscroll_a & 0x7)) & 15);
-				if ((*bg_src & 0x4F) > 0x40) {
-					//background plane has priority and is opaque
-					if (context->debug) {
-						*(dst++) = context->debugcolors[DBG_SRC_A];
-					} else {
-						*(dst++) = context->colors[(*bg_src & 0x1F) + CRAM_SIZE*3];
-					}
-				} else if (*sprite_src) {
-					//sprite layer is opaque
-					if (context->debug) {
-						*(dst++) = context->debugcolors[DBG_SRC_S];
-					} else {
-						*(dst++) = context->colors[*sprite_src | 0x10 + CRAM_SIZE*3];
-					}
-				} else if (*bg_src & 0xF) {
-					//background plane is opaque
+				if ((*bg_src & 0x4F) > 0x40 || !*sprite_src) {
+					//background plane has priority and is opaque or sprite layer is transparent
 					if (context->debug) {
 						*(dst++) = context->debugcolors[DBG_SRC_A];
 					} else {
 						*(dst++) = context->colors[(*bg_src & 0x1F) + CRAM_SIZE*3];
 					}
 				} else {
+					//sprite layer is opaque and not covered by high priority BG pixels
 					if (context->debug) {
-						*(dst++) = context->debugcolors[DBG_SRC_BG];
+						*(dst++) = context->debugcolors[DBG_SRC_S];
 					} else {
-						*(dst++) = context->colors[bgcolor];
+						*(dst++) = context->colors[*sprite_src | 0x10 + CRAM_SIZE*3];
 					}
 				}
 			}