From 10bc0d46600da2d3bd0c0a93ec7c3483d8cee58f Mon Sep 17 00:00:00 2001
From: Doug Lyons <douglyons@douglyons.com>
Date: Mon, 28 Jul 2025 22:00:35 -0500
Subject: [PATCH] [WIN32K:ENG] Fix triangle gradient fill solid color versus
 gradient color selection logic (#8269)

CORE-13532
* Fix macros VCMPCLR and VCMPCLRS to correctly select between gradient color or solid color triangles.
* Remove hack from commit 1c0aedc and replace it with 'if' test before STEPCOL in 'while' test.
* Other assorted fixes for FILLLIINE macro starting position to completely fill triangles.
* Remove warning/FIXME: about IntEngGradientFillTriangle being broken.
* Precede some 'while' loops by 'if' tests to exclude possible loops.
---
 win32ss/gdi/eng/gradient.c | 23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

diff --git a/win32ss/gdi/eng/gradient.c b/win32ss/gdi/eng/gradient.c
index 3fb80c19e35..68c45a3fb38 100644
--- a/win32ss/gdi/eng/gradient.c
+++ b/win32ss/gdi/eng/gradient.c
@@ -18,9 +18,12 @@ const LONG LINC[2] = {-1, 1};
 #define VERTEX(n) (pVertex + gt->n)
 #define COMPAREVERTEX(a, b) ((a)->x == (b)->x && (a)->y == (b)->y)
 
-#define VCMPCLR(a,b,c,color) (a->color != b->color || a->color != c->color)
-#define VCMPCLRS(a,b,c) \
-  !(!VCMPCLR(a,b,c,Red) || !VCMPCLR(a,b,c,Green) || !VCMPCLR(a,b,c,Blue))
+/* Check if all three vectors have the same color, either R, G, or B */
+#define VCMPCLR(a, b, c, color) (a->color == b->color && a->color == c->color)
+/* Check if all three vectors have the same colors for R, G, and B, then
+ * NOT the result because we want to check for not using solid color logic */
+#define VCMPCLRS(a, b, c) \
+  !(VCMPCLR(a, b, c, Red) && VCMPCLR(a, b, c, Green) && VCMPCLR(a, b, c, Blue))
 
 /* Horizontal/Vertical gradients */
 #define HVINITCOL(Col, id) \
@@ -225,6 +228,7 @@ IntEngGradientFillRect(
 
 #define STEPCOL(a,b,line,col,id) \
   ec[line][id] += dc[line][id]; \
+  if(dy[line] != 0) \
   while(ec[line][id] > 0) \
   { \
     c[line][id] += ic[line][id]; \
@@ -239,6 +243,7 @@ IntEngGradientFillRect(
 
 #define FDOCOL(linefrom,lineto,colid) \
   ge[colid] += gd[colid]; \
+  if (gx != 0) \
   while(ge[colid] > 0) \
   { \
     gc[colid] += gi[colid]; \
@@ -251,7 +256,8 @@ IntEngGradientFillRect(
   FINITCOL(linefrom, lineto, 0); \
   FINITCOL(linefrom, lineto, 1); \
   FINITCOL(linefrom, lineto, 2); \
-  for(g = sx[linefrom]; g != sx[lineto]; g += gxi) \
+  g_end = sx[lineto] + gxi; \
+  for(g = sx[linefrom]; g != g_end; g += gxi) \
   { \
     if(InY && g >= FillRect.left && g < FillRect.right) \
     { \
@@ -284,9 +290,9 @@ IntEngGradientFillRect(
 
 #define INITLINE(a,b,line) \
   x[line] = a->x; \
-  sx[line] =  a->x + pptlDitherOrg->x; \
+  sx[line] = a->x + pptlDitherOrg->x - 1; \
   dx[line] = abs(b->x - a->x); \
-  dy[line] = max(abs(b->y - a->y),1); \
+  dy[line] = abs(b->y - a->y); \
   incx[line] = LINC[b->x > a->x]; \
   ex[line] = -(dy[line]>>1); \
   destx[line] = b->x
@@ -331,7 +337,7 @@ IntEngGradientFillTriangle(
     LONG x[NLINES], dx[NLINES], dy[NLINES], incx[NLINES], ex[NLINES], destx[NLINES];
     LONG c[NLINES][3], dc[NLINES][3], ec[NLINES][3], ic[NLINES][3]; /* colors on lines */
     LONG g, gx, gxi, gc[3], gd[3], ge[3], gi[3]; /* colors in triangle */
-    LONG sy, y, bt;
+    LONG sy, y, bt, g_end;
 
     v1 = (pVertex + gTriangle->Vertex1);
     v2 = (pVertex + gTriangle->Vertex2);
@@ -355,8 +361,6 @@ IntEngGradientFillTriangle(
     }
 
     DPRINT("Triangle: (%i,%i) (%i,%i) (%i,%i)\n", v1->x, v1->y, v2->x, v2->y, v3->x, v3->y);
-    /* FIXME: commented out because of an endless loop - fix triangles first */
-    DPRINT("FIXME: IntEngGradientFillTriangle is broken\n");
 
     if (!IntEngEnter(&EnterLeave, psoDest, &FillRect, FALSE, &Translate, &psoOutput))
     {
@@ -396,6 +400,7 @@ IntEngGradientFillTriangle(
               ENDLINE(v1, v2, 1);
 
               GOLINE(v2, v3, 2);
+              FILLLINE(0, 2);
               DOLINE(v2, v3, 2);
               FILLLINE(0, 2);
               ENDLINE(23, v3, 2);