[PATCH v3 0/1] MR10022: gdiplus: Allow GdipBitmapLockBits without read/write flags.

[Bernhard Übelacker (＠bernhardu)]

Wine-Bug: https://bugs.winehq.org/show_bug.cgi?id=59362

[Testbot run with this patch](https://testbot.winehq.org/JobDetails.pl?Key=161700)

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  v3: gdiplus: Allow GdipBitmapLockBits without read/write flags.
 
https://gitlab.winehq.org/wine/wine/-/merge_requests/10022

[PATCH v3 1/1] gdiplus: Allow GdipBitmapLockBits without read/write flags.

[Bernhard Übelacker]

From: Bernhard Übelacker <[e-mail]>

Wine-Bug: https://bugs.winehq.org/show_bug.cgi?id=59362
---
 dlls/gdiplus/image.c       |  2 +-
 dlls/gdiplus/tests/image.c | 60 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 61 insertions(+), 1 deletion(-)

diff --git a/dlls/gdiplus/image.c b/dlls/gdiplus/image.c
index 2449e2ec863..035db159d5b 100644
--- a/dlls/gdiplus/image.c
+++ b/dlls/gdiplus/image.c
@@ -1125,7 +1125,7 @@ GpStatus WINGDIPAPI GdipBitmapLockBits(GpBitmap* bitmap, GDIPCONST GpRect* rect,
 
     if(rect){
         if(rect->X < 0 || rect->Y < 0 || (rect->X + rect->Width > bitmap->width) ||
-          (rect->Y + rect->Height > bitmap->height) || !flags)
+          (rect->Y + rect->Height > bitmap->height))
         {
             image_unlock(&bitmap->image);
             return InvalidParameter;
diff --git a/dlls/gdiplus/tests/image.c b/dlls/gdiplus/tests/image.c
index e3602ceb505..1f4d3ad8876 100644
--- a/dlls/gdiplus/tests/image.c
+++ b/dlls/gdiplus/tests/image.c
@@ -901,6 +901,48 @@ static void test_LockBits(void)
     stat = GdipBitmapSetPixel(bm, 2, 8, 0xff480000);
     expect(Ok, stat);
 
+    /* no read/write flags, no conversion */
+    stat = GdipBitmapLockBits(bm, &rect, 0, PixelFormat24bppRGB, &bd);
+    expect(Ok, stat);
+
+    if (stat == Ok) {
+        expect(0xc3, ((BYTE*)bd.Scan0)[2]);
+        expect(0x48, ((BYTE*)bd.Scan0)[2 + bd.Stride * 5]);
+
+        ((char*)bd.Scan0)[2] = 0xfd;
+
+        stat = GdipBitmapUnlockBits(bm, &bd);
+        expect(Ok, stat);
+    }
+
+    stat = GdipBitmapGetPixel(bm, 2, 3, &color);
+    expect(Ok, stat);
+    expect(0xfffd0000, color);
+
+    stat = GdipBitmapSetPixel(bm, 2, 3, 0xffc30000);
+    expect(Ok, stat);
+
+    /* no read/write flags, conversion */
+    stat = GdipBitmapLockBits(bm, &rect, 0, PixelFormat32bppARGB, &bd);
+    expect(Ok, stat);
+
+    if (stat == Ok) {
+        /* bits appear to be uninitialized */
+
+        ((char*)bd.Scan0)[2] = 0xfe;
+
+        stat = GdipBitmapUnlockBits(bm, &bd);
+        expect(Ok, stat);
+    }
+
+    /* writes do not work if there was a conversion */
+    stat = GdipBitmapGetPixel(bm, 2, 3, &color);
+    expect(Ok, stat);
+    expect(0xffc30000, color);
+
+    stat = GdipBitmapSetPixel(bm, 2, 3, 0xffc30000);
+    expect(Ok, stat);
+
     /* read-only */
     stat = GdipBitmapLockBits(bm, &rect, ImageLockModeRead, PixelFormat24bppRGB, &bd);
     expect(Ok, stat);
@@ -1142,6 +1184,24 @@ static void test_LockBits_UserBuf(void)
     bd.Scan0 = &bits[2+3*WIDTH];
     bd.Reserved = 0xaaaaaaaa;
 
+    /* no read/write flags */
+    stat = GdipBitmapLockBits(bm, &rect, ImageLockModeUserInputBuf, PixelFormat32bppARGB, &bd);
+    expect(Ok, stat);
+
+    expect(0xaaaaaaaa, bits[0]);
+    expect(0xaaaaaaaa, bits[2+3*WIDTH]);
+
+    bits[2+3*WIDTH] = 0xdeadbeef;
+
+    if (stat == Ok) {
+        stat = GdipBitmapUnlockBits(bm, &bd);
+        expect(Ok, stat);
+    }
+
+    stat = GdipBitmapGetPixel(bm, 2, 3, &color);
+    expect(Ok, stat);
+    expect(0, color);
+
     /* read-only */
     stat = GdipBitmapLockBits(bm, &rect, ImageLockModeRead|ImageLockModeUserInputBuf, PixelFormat32bppARGB, &bd);
     expect(Ok, stat);
-- 
GitLab

https://gitlab.winehq.org/wine/wine/-/merge_requests/10022

[Bernhard Übelacker (＠bernhardu)]

On Sat Feb  7 14:46:48 2026 +0000, Esme Povirk wrote:
> We should also test this while requesting a different pixel format so
> that a conversion is required. It's possible that it isn't "supposed" to
> allow writing, but native has an optimization (which we must copy) where
> it will point the caller directly to the bitmap's buffer, which allows
> writing even when the flag isn't specified.
> Thanks for taking a look. I added a conversion to test_LockBits, but to me it looks that neither bits are read from nor wrote back into the bitmap. Is this somewhere near what you had in mind?

-- 
https://gitlab.winehq.org/wine/wine/-/merge_requests/10022#note_129018

[Bernhard Übelacker (＠bernhardu)]

v2/v3:
- Added a case which requires a conversion to test_LockBits.

[Testbot run with this patch](https://testbot.winehq.org/JobDetails.pl?Key=161780)

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https://gitlab.winehq.org/wine/wine/-/merge_requests/10022#note_129019

[Esme Povirk (＠madewokherd)]

On Sat Feb  7 18:11:58 2026 +0000, Bernhard Übelacker wrote:
> Thanks for taking a look. I added a conversion to test_LockBits, but to
> me it looks that neither bits are read from nor wrote back into the
> bitmap. Is this somewhere near what you had in mind?
> Yep, this explains native's behavior pretty well: no read/write access is apparently a valid (though seemingly useless) configuration, and the optimization that points callers directly to the bitmap's backing memory effectively converts that to read+write. And that lines up with the fix.

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https://gitlab.winehq.org/wine/wine/-/merge_requests/10022#note_129034

[PATCH v3 0/1] MR10022: gdiplus: Allow GdipBitmapLockBits without read/write flags. - approved

[Esme Povirk (＠madewokherd)]

This merge request was approved by Esme Povirk.
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https://gitlab.winehq.org/wine/wine/-/merge_requests/10022