I was getting weird results with DrawFocusRect() in a TreeView custom draw routine. The outline was somewhat different, some were almost a solid line and others were dashed. I found out that it's the HDC SetTextColor() value that is affecting it. Even though the selection bars fill color is exactly the same, as I changed various text colors, indeed the drawn outline was different.
I ended up with setting the text color to match the fill color of the highlight bar which gives the same outline the default tree drawing routine gives.
Is this not documented anywhere? Is there even more to it?
Thanks?
DrawFocusRect draws the focus rectangle with a bitwise XOR operation. This is hinted at in the SDK documentation, under the "Remarks" section, where it says:
Because DrawFocusRect is an XOR function, calling it a second time with the same rectangle removes the rectangle from the screen.
This is the whole advantage of DrawFocusRect. It means that you (or the window manager) can draw the focus rectangle and erase it whenever needed without redrawing the entire underlying contents. (This was a big performance win in the era before double-buffering, gobs of memory, fast graphic cards, etc.) The focus rectangle is drawn wherever it needs to be drawn, then, when it needs to be erased, it is just drawn again on top of where it was drawn the first time. The only thing that you (or the window manager) need to keep track of is the coordinates of the rectangle.
You can achieve exactly the same effect as DrawFocusRect by using code like the following to draw an XOR rectangle manually:
void DrawXorRect(HDC hDC, const RECT* prc)
{
// (1)
static const WORD pattern[] = { 0x5555, 0xAAAA,
0x5555, 0xAAAA,
0x5555, 0xAAAA,
0x5555, 0xAAAA,
};
HBITMAP hbmpPattern = CreateBitmap(8, 8, 1, 1, pattern);
// (2)
HBRUSH hbrPattern = CreatePatternBrush(hbmpPattern);
// (3)
HBRUSH hbrOriginal = (HBRUSH)SelectObject(hDC, hbrPattern);
// (4)
UINT cx;
UINT cy;
SystemParametersInfo(SPI_GETFOCUSBORDERWIDTH , 0, &cx, 0);
SystemParametersInfo(SPI_GETFOCUSBORDERHEIGHT, 0, &cy, 0);
// (5)
PatBlt(hDC, prc->left , prc->top , prc->right - prc->left, cy , PATINVERT); // top
PatBlt(hDC, prc->left , prc->bottom - cy, prc->right - prc->left, cy , PATINVERT); // bottom
PatBlt(hDC, prc->left , prc->top + cy, cx , prc->bottom - prc->top - (cy * 2), PATINVERT); // left
PatBlt(hDC, prc->right - cx, prc->top + cy, cx , prc->bottom - prc->top - (cy * 2), PATINVERT); // right
// (6)
SelectObject(hDC, hbrOriginal);
DeleteObject(hbrPattern);
DeleteObject(hbmpPattern);
}
Error-checking has been elided for brevity, but this code does work, and it does mimic DrawFocusRect exactly. (Yes, I even tested it.)
Let's go through the code, step by step, to see what it does, how it works, and what that means:
First, it creates a monochrome 8×8 bitmap (CreateBitmap()) consisting of an alternating pattern of bits (pattern[]): on, off, on, off, etc. (If you don't know why, open up the Windows calculator, switch it to hex mode, and paste in the hex values that comprise the pattern. Look at the bits: see how they alternate between 0s and 1s? Now, imagine creating a bitmap from that.)
Then, it uses that bitmap to create a brush (CreatePatternBrush()).
Next, it selects the newly-created brush into the DC (SelectObject()). It saves the return value, which is the brush that was originally selected in the DC because it needs to restore that later.
With all the drawing objects created, it calls SystemParametersInfo() to retrieve the width (SPI_GETFOCUSBORDER_WIDTH) and height (SPI_GETFOCUSBORDERHEIGHT) of the focus rectangle.
Armed with all the objects and information needed to do the drawing, it blits each of the 4 sides of the rectangle using the PATINVERT raster operation. What is PATINVERT?
Combines the colors of the specified pattern with the colors of the destination rectangle by using the Boolean XOR operator.
Finally, it cleans up after itself by restoring the originally-selected brush and deleting the drawing objects that it created.
So, basically, the focus rectangle is drawn by XORing an alternating pattern of on-and-off pixels (a checkerboard pattern) with the contents of the device context (i.e., whatever is on the screen). That's what PATINVERT does. But wait—we know what the colors of the device context are, but what are the colors of the brush? Well, remember that the brush was created from a monochrome bitmap. The SDK documentation for CreateBitmap says:
If the bitmap is monochrome, zeros represent the foreground color and ones represent the background color for the destination device context.
Aha! So when the brush's bitmap pattern is 0, the brush's color is your device context's foreground color (SetTextColor); when the brush's bitmap pattern is 1, the brush's color is your device context's background color (SetBackColor). This is how the foreground and background color of the device context come into play. These colors are merged together, via an XOR operation, with the color of the original pixel in the device context.
When using DrawFocusRect, your DC's foreground and background colors should be black and white, respectively. This is the default foreground and background colors for a device context, so if you haven't called the SetTextColor or SetBackColor functions, these will be its colors. If you have called either of those functions, you either need to:
Save the value returned by each and restore it later, once you are finished drawing, but before you call DrawFocusRect (just as the code above did with the return value of the first call to SelectObject), or
Call the SaveDC function at the beginning of your drawing code to save its state (by pushing it onto a stack internally), and then call the RestoreDC function at the end of your drawing code to restore it to its original state.
When the DC's foreground and background colors are black and white, respectively, then the DrawFocusRect function works as it is expected to. This is what you need to do if you want to match how the window manager draws focus rectangles around controls. (And you do, obviously, want to do this!)
If, for some reason, you don't want to reset the DC's colors, then you won't be able to use DrawFocusRect. You'll need to take another tack where you control the colors yourself. For example, you could create a color (non-monochrome) bitmap, with its colors fixed as white and black, and then create a brush from that. Alternatively, you could consider drawing with a pen and the R2_NOT ROP code; e.g.:
void DrawXorRect2(HDC hDC, const RECT* prc)
{
LOGBRUSH lb;
lb.lbStyle = BS_SOLID;
lb.lbColor = RGB(0, 0, 0); // black
HPEN hpenNew = ExtCreatePen(PS_COSMETIC | PS_ALTERNATE, 1, &lb, 0, NULL);
HPEN hpenOld = (HPEN)SelectObject(hDC, hpenNew);
int ropOld = SetROP2(hDC, R2_NOT);
int modeOld = SetBkMode(hDC, TRANSPARENT);
HBRUSH hbrOriginal = (HBRUSH)SelectObject(hDC, GetStockObject(NULL_BRUSH));
Rectangle(hDC, prc->left, prc->top, prc->right, prc->bottom);
SelectObject(hDC, hbrOriginal);
SetBkMode(hDC, modeOld);
SetROP2(hDC, ropOld);
SelectObject(hDC, hpenOld);
DeleteObject(hpenNew);
}
I'm not sure this is actually much better, as it still requires that you set attributes of the DC—namely, the ROP and the background mode. If you're going to set and restore attributes of the DC, why not just set and restore the foreground and background colors? Plus, this pen-based implementation has the additional disadvantage of not respecting the user's preference for the thickness of the focus rectangle, which is an accessibility bug. Also, the pixel grid is slightly different here compared to the built-in DrawFocusRect, but that is, admittedly, an extremely minor drawback.
Another approach would be to create a PS_GEOMETRIC pen with a custom pattern (PS_USERSTYLE, to make it alternating), and setting the ROP style to R2_XORPEN/R2_NOTXORPEN:
void DrawXorRect3(HDC hDC, const RECT* prc)
{
UINT cx;
UINT cy;
SystemParametersInfo(SPI_GETFOCUSBORDERWIDTH , 0, &cx, 0);
SystemParametersInfo(SPI_GETFOCUSBORDERHEIGHT, 0, &cy, 0);
LOGBRUSH lb;
lb.lbStyle = BS_SOLID;
lb.lbColor = RGB(0, 0, 0);
static const DWORD pattern[] = { 0, 2 };
HPEN hpenWidth = ExtCreatePen(PS_GEOMETRIC | PS_USERSTYLE, cx, &lb, 2, pattern);
HPEN hpenHeight = ExtCreatePen(PS_GEOMETRIC | PS_USERSTYLE, cy, &lb, 2, pattern);
int ropOriginal = SetROP2(hDC, R2_NOTXORPEN);
HPEN hpenOriginal = (HPEN)SelectObject(hDC, hpenHeight);
MoveToEx(hDC, prc->left , prc->top , NULL); // \ top
LineTo (hDC, prc->right , prc->top ); // / edge
MoveToEx(hDC, prc->left + cx, prc->bottom - cy , NULL); // \ bottom
LineTo (hDC, prc->right - cx, prc->bottom - cy ); // / edge
SelectObject(hDC, hpenWidth);
MoveToEx(hDC, prc->left , prc->top + (cy * 2), NULL); // \ left
LineTo (hDC, prc->left , prc->bottom - cy ); // / edge
MoveToEx(hDC, prc->right - cx, prc->top + cy , NULL); // \ right
LineTo (hDC, prc->right - cx, prc->bottom ); // / edge
SelectObject(hDC, hpenOriginal);
SetROP2(hDC, ropOriginal);
DeleteObject(hpenHeight);
DeleteObject(hpenWidth);
}
This addresses the accessibility bug and makes the pixel pattern match that produced by DrawFocusRect, at the expense of creating an additional pen. It also, like the second attempt, works as expected regardless of what the DC's foreground or background colors are set to.
Note that all of these implementations of DrawXorRect become more efficient if you create the required drawing objects once and cache them, instead of creating and destroying them each time. This is surely a big part of the reason (along with convenience—who wants to write all this ugly code?) why the window manager provides the DrawFocusRect function for applications to use.
I am using the windows GDI API ExtTextOut function to draw text like this:
ExtTextOut(hDC, 2000, 2000, 0, &stRect, PrintText, TextOutLen, aiCharCellDistances);
I am trying to rotate the text, and I do rotate the text. But when I fill the rectangle with colors, I found that the rectangle didn't rotate with the text.
Is there any way to rotate the rectangle with the text? Or is there a better way to do this?
P.S.: My goal is to draw text in the rectangle (like text area) and can rotate it in any angle, and set background color, border line, line break, align right, etc.
Thanks!
It's not 100% clear what you want, but I think you want to draw some text and rectangle rotated at the same angle? If so, it's probably easiest to use SetWorldTransform to do the job.
Here's some code doing it with MFC:
double factor = (2.0f * 3.1416f)/360.0f;
double rot = 45.0f * factor;
// Create a matrix for the transform we want (read the docs for details)
XFORM xfm = { 0.0f };
xfm.eM11 = (float)cos(rot);
xfm.eM12 = (float)sin(rot);
xfm.eM21 = (float)-sin(rot);
xfm.eM22 = (float)cos(rot);
pDC->SetGraphicsMode(GM_ADVANCED);
pDC->SetWorldTransform(&xfm); // Tell Windows to use that transform matrix
pDC->SetBkMode(TRANSPARENT);
CRect rect{ 290, 190, 450, 230 };
CBrush red;
red.CreateSolidBrush(RGB(255, 0, 0));
pDC->FillRect(rect, &red); // Draw a red rectangle behind the text
pDC->TextOut(300, 200, L"This is a string"); // And draw the text at the same angle
For the most part, doing this without MFC just means changing pDC->foo(args) to foo(dc, args).
The result looks like this:
Note that in this case, you do not need to specify rotation (at all--either lfRotation or lfEscapement) for the font you use. You just draw like it was normal text, and the world transform handles all the rotation.
Quick and simple one this time. I have a subclassed tab control that handles WM_WINDOWPOSCHANGED to, when not SWP_NOSIZE, resize its content. It passes the WINDOWPOS lParam's cx and cy fields to TCM_ADJUSTRECT to get the content rect size.
I need to do this on command as well (after changing tabs, say). However, I can't just do a dummy resize to the same size; even with an explicit SetWindowPos(), real Windows seems to add SWP_NOSIZE itself if the size doesn't change. So I want to write the analogous code to my WM_WINDOWPOSCHANGED handler.
My question is: what coordinate system are the coordinates given to WM_WINDOWPOSCHANGED given in, parent coordinates or screen coordinates? GetWindowRect() returns screen coordinates, so I'd like to know if I need to convert the coordinates to get the same values that I would get in WM_WINDOWPOSCHANGED. The documentation for WM_WINDOWPOSCHANGED doesn't say; neither does the documentation for WINDOWPOS.
Thanks.
WINDOWPOS, GetWindowRect, GetCursorPos, etc. give screen coordinates. When you use SetWindowPos you have to supply coordinates in relation to parent. This is straight forward for main window and popup windows which use screen coordinates. For moving child windows, you can use ScreenToClient and ClientToScreen for conversion.
For example, this will find the coordinates of OK button in relation to top-left corner of dialog box:
RECT rcOK;
HWND hitem = ::GetDlgItem(m_hWnd, IDOK);
GetWndRect(rcOK, hitem, m_hWnd);
void GetWndRect(RECT &rect, HWND item, HWND parent)
{
::GetWindowRect(item, &rect);//screen coordinates of OK button
POINT offset{ 0 };
ClientToScreen(parent, &offset); //Top-left (0,0) of client area of dialog -> screen coordinates
rect.left -= offset.x;
rect.right -= offset.x;
rect.top -= offset.y;
rect.bottom -= offset.y;
//client coordinates of OK button in relation to Dialog's Top-Right
}
Now we can move up the OK button by 10px:
rc.top -= 10;
rc.bottom -= 10;
::SetWindowPos(hitem, 0, rc.left, rc.top, 0, 0, SWP_NOSIZE);
I am running this following code,
HDC hdc;
HDC hdcMem;
HBITMAP bitmap;
RECT c;
GetClientRect(viewHandle, &c);
// instead of BeginPaint use GetDC or GetWindowDC
hdc = GetDC(viewHandle);
hdcMem = CreateCompatibleDC(hdc);
// always create the bitmap for the memdc from the window dc
bitmap = CreateCompatibleBitmap(hdc,c.right-c.left,200);
SelectObject(hdcMem, bitmap);
// only execute the code up to this point one time
// that is, you only need to create the back buffer once
// you can reuse it over and over again after that
// draw on hdcMem
// for example ...
Rectangle(hdcMem, 126, 0, 624, 400);
// when finished drawing blit the hdcMem to the hdc
BitBlt(hdc, 0, 0, c.right-c.left,200, hdcMem, 0, 0, SRCCOPY);
// note, height is not spelled i before e
// Clean up - only need to do this one time as well
DeleteDC(hdcMem);
DeleteObject(bitmap);
ReleaseDC(viewHandle, hdc);
The code is just fine. But I am seeing black color around this rectangle. Why is that? Here is an example image.
The bitmap is most likely initialized to be all black. You are then drawing a white rectangle that between x-coordinates 126 and 624. Hence, everything to the left of x=126 and to the right of x=624 stays black.
Edit: The documentation for CreateCompatibleBitmap doesn't state how the bitmap will be initialized, so you should explicitly initialize the bitmap with a specific colour, as Goz suggests, using FillRect:
RECT rc;
rc.left=0;
rc.top=0;
rc.right=c.right-c.left;
rc.bottom=200;
FillRect(hdcMem, &rc, (HBRUSH)GetStockObject(GRAY_BRUSH));
This example fills the bitmap in gray -- you may need to CreateSolidBrush your own brush if you need a different colour. (Don't forget to call DeleteObject when you're done.)
As a side note, I find it a bit strange that your bitmap is being set to a constant height of 200 -- the normal thing would be to make the height of the bitmap equal to the height of the window (as is done for the width).
Might it be because you haven't initialised the memory bitmap area to a given colour? Try FillRect'ing the background to a different colour then draw your white rectangle over it and see what happens.
Per MSDN http://msdn.microsoft.com/en-us/library/dd162898.aspx:
The rectangle is outlined by using the current pen and filled by using the current brush.
Consider calling FillRect instead, or select an appropriate pen prior to calling Rectangle'.
I used:
// Fill the background
hdcMem->FillSolidRect(c, hdcMem->GetBkColor());
Just as a note.