[PATCH] windowscodecs: Fix rounding in premultiplied alpha conversion.

[Jinoh Kang]

Signed-off-by: Jinoh Kang <jinoh.kang.kr(a)gmail.com>
---
 dlls/windowscodecs/converter.c       | 12 ++++-----
 dlls/windowscodecs/tests/converter.c | 38 +++++++++++++++++++++++-----
 2 files changed, 37 insertions(+), 13 deletions(-)

diff --git a/dlls/windowscodecs/converter.c b/dlls/windowscodecs/converter.c
index 8abba2dec52..e93606e938d 100644
--- a/dlls/windowscodecs/converter.c
+++ b/dlls/windowscodecs/converter.c
@@ -984,9 +984,9 @@ static HRESULT copypixels_to_32bppPBGRA(struct FormatConverter *This, const WICR
                     BYTE alpha = pbBuffer[cbStride*y+4*x+3];
                     if (alpha != 255)
                     {
-                        pbBuffer[cbStride*y+4*x] = pbBuffer[cbStride*y+4*x] * alpha / 255;
-                        pbBuffer[cbStride*y+4*x+1] = pbBuffer[cbStride*y+4*x+1] * alpha / 255;
-                        pbBuffer[cbStride*y+4*x+2] = pbBuffer[cbStride*y+4*x+2] * alpha / 255;
+                        pbBuffer[cbStride*y+4*x] = (pbBuffer[cbStride*y+4*x] * alpha + 127) / 255;
+                        pbBuffer[cbStride*y+4*x+1] = (pbBuffer[cbStride*y+4*x+1] * alpha + 127) / 255;
+                        pbBuffer[cbStride*y+4*x+2] = (pbBuffer[cbStride*y+4*x+2] * alpha + 127) / 255;
                     }
                 }
         }
@@ -1017,9 +1017,9 @@ static HRESULT copypixels_to_32bppPRGBA(struct FormatConverter *This, const WICR
                     BYTE alpha = pbBuffer[cbStride*y+4*x+3];
                     if (alpha != 255)
                     {
-                        pbBuffer[cbStride*y+4*x] = pbBuffer[cbStride*y+4*x] * alpha / 255;
-                        pbBuffer[cbStride*y+4*x+1] = pbBuffer[cbStride*y+4*x+1] * alpha / 255;
-                        pbBuffer[cbStride*y+4*x+2] = pbBuffer[cbStride*y+4*x+2] * alpha / 255;
+                        pbBuffer[cbStride*y+4*x] = (pbBuffer[cbStride*y+4*x] * alpha + 127) / 255;
+                        pbBuffer[cbStride*y+4*x+1] = (pbBuffer[cbStride*y+4*x+1] * alpha + 127) / 255;
+                        pbBuffer[cbStride*y+4*x+2] = (pbBuffer[cbStride*y+4*x+2] * alpha + 127) / 255;
                     }
                 }
         }
diff --git a/dlls/windowscodecs/tests/converter.c b/dlls/windowscodecs/tests/converter.c
index 9159141d6e5..2e77db6b205 100644
--- a/dlls/windowscodecs/tests/converter.c
+++ b/dlls/windowscodecs/tests/converter.c
@@ -453,13 +453,21 @@ static const BYTE bits_32bppBGR[] = {
     0,255,255,80, 255,0,255,80, 255,255,0,80, 255,255,255,80, 0,255,255,80, 255,0,255,80, 255,255,0,80, 255,255,255,80,
     0,255,255,80, 255,0,255,80, 255,255,0,80, 255,255,255,80, 0,255,255,80, 255,0,255,80, 255,255,0,80, 255,255,255,80,
     0,255,255,80, 255,0,255,80, 255,255,0,80, 255,255,255,80, 0,255,255,80, 255,0,255,80, 255,255,0,80, 255,255,255,80,
-    0,255,255,80, 255,0,255,80, 255,255,0,80, 255,255,255,80, 0,255,255,80, 255,0,255,80, 255,255,0,80, 255,255,255,80};
+    0,255,255,80, 255,0,255,80, 255,255,0,80, 255,255,255,80, 0,255,255,80, 255,0,255,80, 255,255,0,80, 255,255,255,80,
+    3,3,3,80, 6,6,6,80, 12,12,12,80, 15,15,15,80, 19,19,19,80, 22,22,22,80, 28,28,28,80, 31,31,31,80,
+    35,35,35,80, 38,38,38,80, 41,41,41,80, 47,47,47,80, 47,47,47,80, 54,54,54,80, 57,57,57,80, 63,63,63,80,
+    66,66,66,80, 70,70,70,80, 73,73,73,80, 79,79,79,80, 82,82,82,80, 86,86,86,80, 89,89,89,80, 95,95,95,80,
+    98,98,98,80, 98,98,98,80, 105,105,105,80, 108,108,108,80, 114,114,114,80, 117,117,117,80, 121,121,121,80, 124,124,124,80,
+    130,130,130,80, 133,133,133,80, 137,137,137,80, 140,140,140,80, 146,146,146,80, 149,149,149,80, 156,156,156,80, 156,156,156,80,
+    159,159,159,80, 165,165,165,80, 168,168,168,80, 172,172,172,80, 175,175,175,80, 181,181,181,80, 184,184,184,80, 188,188,188,80,
+    191,191,191,80, 197,197,197,80, 200,200,200,80, 207,207,207,80, 207,207,207,80, 213,213,213,80, 216,216,216,80, 219,219,219,80,
+    223,223,223,80, 226,226,226,80, 232,232,232,80, 235,235,235,80, 239,239,239,80, 242,242,242,80, 248,248,248,80, 251,251,251,80};
 static const struct bitmap_data testdata_32bppBGR = {
     &GUID_WICPixelFormat32bppBGR, 32, bits_32bppBGR, 32, 2, 96.0, 96.0};
 static const struct bitmap_data testdata_32bppBGRA80 = {
-    &GUID_WICPixelFormat32bppBGRA, 32, bits_32bppBGR, 32, 2, 96.0, 96.0};
+    &GUID_WICPixelFormat32bppBGRA, 32, bits_32bppBGR, 32, 4, 96.0, 96.0};
 static const struct bitmap_data testdata_32bppRGBA80 = {
-    &GUID_WICPixelFormat32bppRGBA, 32, bits_32bppBGR, 32, 2, 96.0, 96.0};
+    &GUID_WICPixelFormat32bppRGBA, 32, bits_32bppBGR, 32, 4, 96.0, 96.0};
 
 static const BYTE bits_32bppBGRA[] = {
     255,0,0,255, 0,255,0,255, 0,0,255,255, 0,0,0,255, 255,0,0,255, 0,255,0,255, 0,0,255,255, 0,0,0,255,
@@ -469,7 +477,15 @@ static const BYTE bits_32bppBGRA[] = {
     0,255,255,255, 255,0,255,255, 255,255,0,255, 255,255,255,255, 0,255,255,255, 255,0,255,255, 255,255,0,255, 255,255,255,255,
     0,255,255,255, 255,0,255,255, 255,255,0,255, 255,255,255,255, 0,255,255,255, 255,0,255,255, 255,255,0,255, 255,255,255,255,
     0,255,255,255, 255,0,255,255, 255,255,0,255, 255,255,255,255, 0,255,255,255, 255,0,255,255, 255,255,0,255, 255,255,255,255,
-    0,255,255,255, 255,0,255,255, 255,255,0,255, 255,255,255,255, 0,255,255,255, 255,0,255,255, 255,255,0,255, 255,255,255,255};
+    0,255,255,255, 255,0,255,255, 255,255,0,255, 255,255,255,255, 0,255,255,255, 255,0,255,255, 255,255,0,255, 255,255,255,255,
+    3,3,3,255, 6,6,6,255, 12,12,12,255, 15,15,15,255, 19,19,19,255, 22,22,22,255, 28,28,28,255, 31,31,31,80,
+    35,35,35,255, 38,38,38,255, 41,41,41,255, 47,47,47,255, 47,47,47,255, 54,54,54,255, 57,57,57,255, 63,63,63,80,
+    66,66,66,255, 70,70,70,255, 73,73,73,255, 79,79,79,255, 82,82,82,255, 86,86,86,255, 89,89,89,255, 95,95,95,80,
+    98,98,98,255, 98,98,98,255, 105,105,105,255, 108,108,108,255, 114,114,114,255, 117,117,117,255, 121,121,121,255, 124,124,124,80,
+    130,130,130,255, 133,133,133,255, 137,137,137,255, 140,140,140,255, 146,146,146,255, 149,149,149,255, 156,156,156,255, 156,156,156,80,
+    159,159,159,255, 165,165,165,255, 168,168,168,255, 172,172,172,255, 175,175,175,255, 181,181,181,255, 184,184,184,255, 188,188,188,80,
+    191,191,191,255, 197,197,197,255, 200,200,200,255, 207,207,207,255, 207,207,207,255, 213,213,213,255, 216,216,216,255, 219,219,219,80,
+    223,223,223,255, 226,226,226,255, 232,232,232,255, 235,235,235,255, 239,239,239,255, 242,242,242,255, 248,248,248,255, 251,251,251,80};
 static const BYTE bits_32bppRGBA[] = {
     0,0,255,255, 0,255,0,255, 255,0,0,255, 0,0,0,255, 0,0,255,255, 0,255,0,255, 255,0,0,255, 0,0,0,255,
     0,0,255,255, 0,255,0,255, 255,0,0,255, 0,0,0,255, 0,0,255,255, 0,255,0,255, 255,0,0,255, 0,0,0,255,
@@ -495,11 +511,19 @@ static const BYTE bits_32bppPBGRA[] = {
     0,80,80,80, 80,0,80,80, 80,80,0,80, 80,80,80,80, 0,80,80,80, 80,0,80,80, 80,80,0,80, 80,80,80,80,
     0,80,80,80, 80,0,80,80, 80,80,0,80, 80,80,80,80, 0,80,80,80, 80,0,80,80, 80,80,0,80, 80,80,80,80,
     0,80,80,80, 80,0,80,80, 80,80,0,80, 80,80,80,80, 0,80,80,80, 80,0,80,80, 80,80,0,80, 80,80,80,80,
-    0,80,80,80, 80,0,80,80, 80,80,0,80, 80,80,80,80, 0,80,80,80, 80,0,80,80, 80,80,0,80, 80,80,80,80};
+    0,80,80,80, 80,0,80,80, 80,80,0,80, 80,80,80,80, 0,80,80,80, 80,0,80,80, 80,80,0,80, 80,80,80,80,
+    1,1,1,80, 2,2,2,80, 4,4,4,80, 5,5,5,80, 6,6,6,80, 7,7,7,80, 9,9,9,80, 10,10,10,80,
+    11,11,11,80, 12,12,12,80, 13,13,13,80, 15,15,15,80, 15,15,15,80, 17,17,17,80, 18,18,18,80, 20,20,20,80,
+    21,21,21,80, 22,22,22,80, 23,23,23,80, 25,25,25,80, 26,26,26,80, 27,27,27,80, 28,28,28,80, 30,30,30,80,
+    31,31,31,80, 31,31,31,80, 33,33,33,80, 34,34,34,80, 36,36,36,80, 37,37,37,80, 38,38,38,80, 39,39,39,80,
+    41,41,41,80, 42,42,42,80, 43,43,43,80, 44,44,44,80, 46,46,46,80, 47,47,47,80, 49,49,49,80, 49,49,49,80,
+    50,50,50,80, 52,52,52,80, 53,53,53,80, 54,54,54,80, 55,55,55,80, 57,57,57,80, 58,58,58,80, 59,59,59,80,
+    60,60,60,80, 62,62,62,80, 63,63,63,80, 65,65,65,80, 65,65,65,80, 67,67,67,80, 68,68,68,80, 69,69,69,80,
+    70,70,70,80, 71,71,71,80, 73,73,73,80, 74,74,74,80, 75,75,75,80, 76,76,76,80, 78,78,78,80, 79,79,79,80};
 static const struct bitmap_data testdata_32bppPBGRA = {
-    &GUID_WICPixelFormat32bppPBGRA, 32, bits_32bppPBGRA, 32, 2, 96.0, 96.0};
+    &GUID_WICPixelFormat32bppPBGRA, 32, bits_32bppPBGRA, 32, 4, 96.0, 96.0};
 static const struct bitmap_data testdata_32bppPRGBA = {
-    &GUID_WICPixelFormat32bppPRGBA, 32, bits_32bppPBGRA, 32, 2, 96.0, 96.0};
+    &GUID_WICPixelFormat32bppPRGBA, 32, bits_32bppPBGRA, 32, 4, 96.0, 96.0};
 
 static const BYTE bits_64bppRGBA[] = {
     128,0,128,0,128,255,128,255, 128,0,128,255,128,0,128,255, 128,255,128,0,128,0,128,255, 128,0,128,0,128,0,128,255, 128,0,128,0,128,255,128,255, 128,0,128,255,128,0,128,255, 128,255,128,0,128,0,128,255, 128,0,128,0,128,0,128,255,
-- 
2.34.1

[Esme Povirk (she/they)]

Signed-off-by: Esme Povirk <esme(a)codeweavers.com>