Correction for negative affine parallax

core/vip.c

@@ -41,16 +41,17 @@ static const uint8_t BG_TEMPLATES[][64] = {
 };
 
 /* 8-bit color magnitude by brightness level */
+/* Generated as BRIGHT8[n] = round((n / 132) ** 1.6 * 255) */
 static const uint8_t BRIGHT8[] = {
-      0,  1,  3,  5,  7,  9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 28,
-     30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 57, 59,
-     61, 63, 65, 67, 69, 71, 73, 75, 77, 79, 81, 83, 85, 86, 88, 90,
-     92, 94, 96, 98,100,102,104,106,108,110,112,113,115,117,119,121,
-    123,125,127,129,131,133,135,137,139,141,142,144,146,148,150,152,
-    154,156,158,160,162,164,166,168,170,171,173,175,177,179,181,183,
-    185,187,189,191,193,195,197,198,200,202,204,206,208,210,212,214,
-    216,218,220,222,224,226,227,229,231,233,235,237,239,241,243,245,
-    247,249,251,253,255
+      0, 12, 19, 24, 29, 33, 37, 41, 44, 48, 51, 54, 57, 60, 63, 65,
+     68, 71, 73, 76, 78, 81, 83, 86, 88, 90, 92, 95, 97, 99,101,103,
+    105,107,109,111,113,115,117,119,121,123,125,127,128,130,132,134,
+    136,137,139,141,142,144,146,148,149,151,153,154,156,157,159,161,
+    162,164,165,167,168,170,172,173,175,176,178,179,181,182,184,185,
+    186,188,189,191,192,194,195,197,198,199,201,202,203,205,206,208,
+    209,210,212,213,214,216,217,218,220,221,222,224,225,226,228,229,
+    230,231,233,234,235,236,238,239,240,242,243,244,245,246,248,249,
+    250,251,253,254,255
 };
 
 
@@ -1004,7 +1005,7 @@ static void vipDrawAffine(VB *sim, World *world) {
     Cell    *cell;               /* Source cell */
     uint8_t *col, *row;          /* Output pixel */
     uint8_t  pixel;              /* Character pixel value */
-    uint8_t *param;              /* World parameter memory */
+    uint32_t param;              /* World parameter memory */
     int32_t  px, py;             /* Pixel source coordinates */
     int32_t  dx, dy, mp, mx, my; /* Affine parameters */
     int32_t  wx;                 /* Base world X coordinate */
@@ -1051,21 +1052,26 @@ static void vipDrawAffine(VB *sim, World *world) {
         wx = x1 - wx;
 
         /* Process all visible rows */
-        param = &sim->vip.ram[world->paramBase | (y1 - world->gy) << 4];
+        param = world->paramBase + ((y1 - world->gy) << 4);
         row   = &sim->vip.shadow[i][x1 * 224 + y1];
         for (y = y1; y < y2; y++, param += 16, row++) {
 
             /* Parse line parameters */
-            mx = (int32_t) busReadBuffer(param + 0, VB_S16) << 6;
-            mp = (int32_t) busReadBuffer(param + 2, VB_S16);
-            my = (int32_t) busReadBuffer(param + 4, VB_S16) << 6;
-            dx = (int32_t) busReadBuffer(param + 6, VB_S16);
-            dy = (int32_t) busReadBuffer(param + 8, VB_S16);
+            mx = (int32_t) busReadBuffer(&sim->vip.ram[param | 0], VB_S16) << 6;
+            mp = (int32_t) busReadBuffer(&sim->vip.ram[param | 2], VB_S16);
+            my = (int32_t) busReadBuffer(&sim->vip.ram[param | 4], VB_S16) << 6;
+            dx = (int32_t) busReadBuffer(&sim->vip.ram[param | 6], VB_S16);
+            dy = (int32_t) busReadBuffer(&sim->vip.ram[param | 8], VB_S16);
 
             /* Adjust left-edge parameters */
             if ((mp < 0) ^ i) {
+                if (mp < 0) {
+                    mx += dx * (wx - mp);
+                    my += dy * (wx - mp);
+                } else {
                     mx += dx * (wx + mp);
                     my += dy * (wx + mp);
+                }
             } else {
                 mx += dx * wx;
                 my += dy * wx;