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Inconsistent vertical spacing of trackbars in WinAPI HighGUI backend #22766

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#22805
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Inconsistent vertical spacing of trackbars in WinAPI HighGUI backend#22766
#22805
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bugcategory: highgui-gui
Milestone
3.4.19
@dan-masek

Description

@dan-masek
dan-masek
opened on Nov 8, 2022

Windows 10, OpenCV 4.6.0 (and many more)

Once more than 2 trackbars are added, it becomes evident that the vertical spacing between them is not consistent:
image

In more detail (further rows also have 21 pixels):
image

The culprit is an off-by-one error on line 2434:

opencv/modules/highgui/src/window_w32.cpp

Lines 2431 to 2447 in 2aad039

/* Retrieve current buttons count */
int bcount = (int)SendMessage(window.toolbar.toolbar, TB_BUTTONCOUNT, 0, 0);
if (bcount > 1)
{
/* If this is not the first button then we need to
separate it from the previous one */
tbs.iBitmap = 0;
tbs.idCommand = bcount; // Set button id to it's number
tbs.iString = 0;
tbs.fsStyle = TBSTYLE_SEP;
tbs.fsState = TBSTATE_ENABLED;
SendMessage(window.toolbar.toolbar, TB_ADDBUTTONS, 1, (LPARAM)&tbs);
// Retrieve current buttons count
bcount = (int)SendMessage(window.toolbar.toolbar, TB_BUTTONCOUNT, 0, 0);
}

Once there is at least 1 button, a separator should be added, hence if (bcount > 0).

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