I use different WinGDI-functions to send data to the printer, here vector data are sent using function Polyline(). Now I want to set a color for this polyline, so I tried calling functions SetDCPenColor() and SetDCBrushColor() prior to the Polyline()-call.
Unfortunately none of them had any influence, the resulting lines are still black. So...what could be wrong here? Which is the correct function to change the colour of such a polyline?
Thanks!
Edit: the code which does not work
SetDCPenColor(*pdc,RGB(rval,gval,bval));
Polyline(*pdc,points,n);
Setting the DC pen and brush colors doesn't have any effect unless you have the DC pen and/or brush selected into the DC. They are not selected into the DC by default.
PAINTSTRUCT ps;
::BeginPaint(hwnd, &ps);
::SetDCPenColor(ps.hdc, RGB(0xFF, 0x00, 0x00)); // has no effect
::MoveToEx(ps.hdc, x0, y0, nullptr);
::LineTo(ps.hdc, x1, y1);
::EndPaint(hwnd, &ps);
To use the DC pen or brush, you need to first select the DC object into the DC.
PAINTSTRUCT ps;
::BeginPaint(hwnd, &ps);
auto oldPen = ::SelectObject(ps.hdc, ::GetStockObject(DC_PEN)); // <<<<
::SetDCPenColor(ps.hdc, RGB(0xFF, 0x00, 0x00)); // now this works
::MoveToEx(ps.hdc, x0, y0, nullptr);
::LineTo(ps.hdc, x1, y1);
::SelectObject(ps.hdc, oldPen); // remember to select it back out
::EndPaint(hwnd, &ps);
Related
The Win32 API function CreateFont() documentation has a confusing example:
As you can see below, they made 3 calls to CreateFont() using the same HANDLE (hFont).. and at the end they have called DeleteObject() for the last one only... but before EndPaint() (while the font is being select to the DC).
I've found this example so misleading about the way DeleteObject() must be used.
I hope if someone could confirm or justify this code.
The example:
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
int wmId, wmEvent;
PAINTSTRUCT ps;
HDC hdc;
switch (message)
{
case WM_PAINT:
{
RECT rect;
HBRUSH hBrush;
HFONT hFont;
hdc = BeginPaint(hWnd, &ps);
//Logical units are device dependent pixels, so this will create a handle to a logical font that is 48 pixels in height.
//The width, when set to 0, will cause the font mapper to choose the closest matching value.
//The font face name will be Impact.
hFont = CreateFont(48,0,0,0,FW_DONTCARE,FALSE,TRUE,FALSE,DEFAULT_CHARSET,OUT_OUTLINE_PRECIS,
CLIP_DEFAULT_PRECIS,CLEARTYPE_QUALITY, VARIABLE_PITCH,TEXT("Impact"));
SelectObject(hdc, hFont);
//Sets the coordinates for the rectangle in which the text is to be formatted.
SetRect(&rect, 100,100,700,200);
SetTextColor(hdc, RGB(255,0,0));
DrawText(hdc, TEXT("Drawing Text with Impact"), -1,&rect, DT_NOCLIP);
//Logical units are device dependent pixels, so this will create a handle to a logical font that is 36 pixels in height.
//The width, when set to 20, will cause the font mapper to choose a font which, in this case, is stretched.
//The font face name will be Times New Roman. This time nEscapement is at -300 tenths of a degree (-30 degrees)
hFont = CreateFont(36,20,-300,0,FW_DONTCARE,FALSE,TRUE,FALSE,DEFAULT_CHARSET,OUT_OUTLINE_PRECIS,
CLIP_DEFAULT_PRECIS,CLEARTYPE_QUALITY, VARIABLE_PITCH,TEXT("Times New Roman"));
SelectObject(hdc,hFont);
//Sets the coordinates for the rectangle in which the text is to be formatted.
SetRect(&rect, 100, 200, 900, 800);
SetTextColor(hdc, RGB(0,128,0));
DrawText(hdc, TEXT("Drawing Text with Times New Roman"), -1,&rect, DT_NOCLIP);
//Logical units are device dependent pixels, so this will create a handle to a logical font that is 36 pixels in height.
//The width, when set to 10, will cause the font mapper to choose a font which, in this case, is compressed.
//The font face name will be Arial. This time nEscapement is at 250 tenths of a degree (25 degrees)
hFont = CreateFont(36,10,250,0,FW_DONTCARE,FALSE,TRUE,FALSE,DEFAULT_CHARSET,OUT_OUTLINE_PRECIS,
CLIP_DEFAULT_PRECIS,ANTIALIASED_QUALITY, VARIABLE_PITCH,TEXT("Arial"));
SelectObject(hdc,hFont);
//Sets the coordinates for the rectangle in which the text is to be formatted.
SetRect(&rect, 500, 200, 1400, 600);
SetTextColor(hdc, RGB(0,0,255));
DrawText(hdc, TEXT("Drawing Text with Arial"), -1,&rect, DT_NOCLIP);
DeleteObject(hFont);
EndPaint(hWnd, &ps);
break;
}
case WM_DESTROY:
PostQuitMessage(0);
break;
default:
return DefWindowProc(hWnd, message, wParam, lParam);
}
return 0;
}
I'm supposed to write an application using win32 API which draws a function f(x)= x^2 plot. To accomplish this I'm asked to use HBRUSH structure, but there seems to be no appropriate procedure in win32 API. There are tons of them mostly used to draw complete shapes.
Is there one I can use to draw my plot point by point?
Brush is intended to draw surfaces, rect areas, filling, etc; you really need pens
Try this:
HDC hdc = /* init this */;
HPEN pen = CreatePen(PS_SOLID, 0, RGB(0, 0, 0));
HGDIOBJ old_pen = SelectObject(hdc, pen);
// move to first poing in plot
MoveToEx(hdc, startingpoint_x, statingpoint_y, NULL);
// executes for each point in plot
LineTo(hdc, pointx, pointy);
// clean up
SelectObject(hdc, old_pen);
DeleteObject(pen);
I'm studying Drawing Shapes by WinAPI C++
I tried to draw 2 ellipse with some codes on WM_PAINT:
PAINTSTRUCT ps;
HDC hdc = BeginPaint(hWnd, &ps);
HPEN hPen = CreatePen(PS_DASHDOTDOT, 2, NULL);SelectObject(hdc, hPen);
Ellipse(hdc, 100, 200, 400, 400);
Ellipse(hdc, 300, 300, 500, 510);
DeleteObject(hPen);
EndPaint(hWnd, &ps);
But the output is:
The result I expect is neither shapes is front of the other. And the border is dash dot dot.
Can anyone show me my mistake? I appreciate for your help.
Ellipse() (like all GDI shape functions) fills the shape using the current brush, which is why your output looks like that. For details on that see setting pen and brush colors.
If you want just the ellipse with no fill, first select a null brush:
SelectObject( hdc, GetStockObject( NULL_BRUSH ) );
One appears on top of the other because you're not just drawing the outline, but filling it as well. To stop filling it, you can select a "hollow brush", sometimes called a "null brush".
HBRUSH hbrOld = SelectObject(hdc, GetStockObject(HOLLOW_BRUSH));
// draw your ellipses here
You can only create dotted or dashed pens with widths of 1 or 0. You used 2, so the command failed.
Also, you should select the pen back out of the DC before you delete it.
I want to know how to write text on a particular window starting at a given location in the window using the Windows API.
For example if the coordinates within the window where the text is to be written are (x,y) = (40,10) then what do I need to do to write a line of text to a particular window at that location in the window?
Suppose your window name is "hwnd" and the text which u want to write on that window at x,y coordinate is say stored in "message" where
LPCWSTR message=L"My First Window"; then
RECT rect;
HDC wdc = GetWindowDC(hwnd);
GetClientRect (bgHandle, &rect) ;
SetTextColor(wdc, 0x00000000);
SetBkMode(wdc,TRANSPARENT);
rect.left=40;
rect.top=10;
DrawText( wdc, message, -1, &rect, DT_SINGLELINE | DT_NOCLIP ) ;
DeleteDC(wdc);
Thats it.. remember this is just one example.
I am hoping this a more complete answer...
void OnPaint(HWND hWnd)
{
RECT rect;
PAINTSTRUCT ps;
HDC hdc = BeginPaint(hWnd, &ps);
GetClientRect(hWnd, &rect);
SetTextColor(hdc, RGB(0xFF, 0x00, 0x00));
SetBkMode(hdc, TRANSPARENT);
rect.left = 40;
rect.top = 10;
DrawText(hdc, L"Hello World!", -1, &rect, DT_SINGLELINE | DT_NOCLIP);
SelectObject(hdc, oldPen);
DeleteObject(hPen);
EndPaint(hWnd, &ps);
}
This would then be called from the WM_PAINT message in the WndProc.
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.