So my teacher gave us a chunk of code to use for double buffering.
He said "here, use this code so you don't have to sit there for hours finding out how"
Except his code does not function.
His initial usage of hdc is undefined. I tried putting it in the parameter list but that is a no go.
This is the code he gave us:
// Create a backbufer bmp bufer to draw to in memory.
RECT rcClient;
::GetClientRect(hwnd, &rcClient);
int left = rcClient.left;
int top = rcClient.top;
int width = rcClient.right - rcClient.left;
int height = rcClient.bottom - rcClient.top;
HDC hdcMem = ::CreateCompatibleDC(hdc);
const int nMemDC = ::SaveDC(hdcMem);
HBITMAP hBitmap = ::CreateCompatibleBitmap(hdc, width, height);
::SelectObject(hdcMem, hBitmap);
Graphics graphics(hdcMem);
SolidBrush back(Color(255,255,255));
graphics.FillRectangle(&back, left, top, width, height);
// Draw to backbufer bitmap here.
// End draw to backbufer bitmap bufer.
// Swap bufers ie. push memory backbufer to the screen frontbufer
RECT rcClip;
::GetClipBox(hdc, &rcClip);
left = rcClip.left;
top = rcClip.top;
width = rcClip.right - rcClip.left;
height = rcClip.bottom - rcClip.top;
::BitBlt(hdc, left, top, width, height, hdcMem, left, top, SRCCOPY);
::RestoreDC(hdcMem, nMemDC);
::DeleteObject(hBitmap);
Right here is where I run into the errors: HDC hdcMem = ::CreateCompatibleDC(hdc);
I attempted declaring an HDC like so
HDC hdc = (HDC)BeginPaint((LPPAINTSTRUCT)AfxGetApp()->m_pMainWnd->GetSafeHwnd());
But that doesn't compile. What do I do with this hdc?
The HDC is returned by BeginPaint, which presumably is called immediately before this code. BeginPaint takes two parameters and you are trying to call it with only one parameter. Do you have earlier exercises where you handled BeginPaint?
So thanks to the various answers here. My knowledge of this is still fairly new, however with the help of my class mates I was able to come to a solution. Sadly I still do not know what to do with the HDC and this was the first of my problems,
HDC hdcMem = ::CreateCompatibleDC(hdc); was able to be replaced by
HDC hdcMem = ::CreateCompatibleDC(dc);
and a lot of the other code that produced warnings such as the hwnd was simply removed and it worked fine.
Related
I have created a second desktop using CreateDesktop and im not switching to it. Also i have created some processes in it like Explorer.exe and Winrar.exe. Next i have a code which takes Screenshot of current desktop to clipboard. Both CreateDesktop and Screenshot works, But Screenshot of that new desktop or window returns a black bitmap:
This is the screenshot for a window in a desktop which returns current desktop:
// hwnd is handle to winrar or ... created in a new desktop retrieved by EnumDesktopWindow
RECT rc;
GetClientRect(hwnd, &rc);
const HDC hScreenDC = GetDC(nullptr);
const HDC hMemoryDC = CreateCompatibleDC(hScreenDC);
const int width = GetDeviceCaps(hScreenDC, HORZRES);
const int height = GetDeviceCaps(hScreenDC, VERTRES);
const HBITMAP hBitmap = CreateCompatibleBitmap(hScreenDC, width, height);
HBITMAP(SelectObject(hMemoryDC, hBitmap));
BitBlt(hMemoryDC, 0, 0, width, height, hScreenDC, 0, 0, SRCCOPY);
OpenClipboard(nullptr);
EmptyClipboard();
SetClipboardData(CF_BITMAP, hBitmap);
CloseClipboard();
DeleteDC(hMemoryDC);
DeleteDC(hScreenDC);
I have implemented both this methods in c# but same thing happens there.
There are great resources like:
Capture screenshot of hidden desktop
take a screenshot of a desktop created using createdesktop api
C# – SCREEN CAPTURE WITH VISTA DWM (SHARED DIRECT3D SURFACE)
Window Contents Capturing using WM_PRINT Message
how to capture screen from another desktop?(CreateDesktop)
Also this is like a dead topic, No new article, Explanation or solution to it.
I have read most of them but no luck, This was my closest try i think. Also language doesnt matter for me: C#, C++, Python or ... .
I found the solution, It is interesting but no perfect, Just resolves my needs.
After CreateDesktop by calling OpenDesktop then SetThreadDesktop then using the screenshot code you get the screenshot of the window which is created inside CreateDesktop, Also no need for Creating Explorer.exe inside it if you just want the window:
CreateDesktopW(L"NewDesktop"); // CreateDesktop code here. This is my function
const HDESK Handle = OpenDesktopW(L"NewDesktop", 0, 0, GENERIC_ALL);
SetThreadDesktop(Handle);
// Above ScreenShot code here ...
The screenshot code needs a PrintWindow:
RECT rc;
GetClientRect(hwnd, &rc);
const HDC hScreenDC = GetDC(nullptr);
const HDC hMemoryDC = CreateCompatibleDC(hScreenDC);
const int width = GetDeviceCaps(hScreenDC, HORZRES);
const int height = GetDeviceCaps(hScreenDC, VERTRES);
const HBITMAP hBitmap = CreateCompatibleBitmap(hScreenDC, width, height);
HBITMAP(SelectObject(hMemoryDC, hBitmap));
BitBlt(hMemoryDC, 0, 0, width, height, hScreenDC, 0, 0, SRCCOPY);
/// ADDED CODE
PrintWindow(hWnd, hMemoryDC, PW_CLIENTONLY);
///
OpenClipboard(nullptr);
EmptyClipboard();
SetClipboardData(CF_BITMAP, hBitmap);
CloseClipboard();
DeleteDC(hMemoryDC);
DeleteDC(hScreenDC);
Mine worked with a winrar.exe window inside a inactive desktop. You can try this then paste it to paint to see the result.
There is just one thing, The whole area of the screenshot bitmap is black except the window handle that i want which is fine by me. I think i should get handle of every window from bottom to top in order then mix them up.
All additions to this are appreciated.
INTRODUCTION:
I am building small app that displays .emf (Enhanced Windows Metafile) in a window.
If image can not fit inside window, scroll bars will be used to show the invisible parts.
Since I am dealing with metafiles, I am trying to add zooming as well.
RELEVANT INFORMATION:
I am playing an .emf file (from the disk) in memory device context (created with the CreateCompatibleDC API). Then I use BitBlt API to transfer that image into main window's client area. I am doing all this to avoid flickering.
Reading through the MSDN I found documentation about Using Coordinate Spaces and Transformations and immediately realized its potential for solving my task of scaling / scrolling the metafile.
PROBLEM:
I do not know how to use before mentioned APIs to scale / scroll metafile inside memory device context, so I can BitBlt that image into main window's device context (this is my first time tackling this type of task).
MY EFFORTS TO SOLVE THE PROBLEM:
I have experimented with XFORM matrix to achieve scaling, like this:
case WM_ERASEBKGND: // prevents flickering
return 1L;
case WM_PAINT:
{
hdc = BeginPaint(hWnd, &ps);
// get main window's client rectangle
RECT rc = { 0 };
GetClientRect(hWnd, &rc);
// fill rectangle with gray brush
// this is necessery because I have bypassed WM_ERASEBKGND,
// see above
FillRect(hdc, &rc, (HBRUSH)GetStockObject(LTGRAY_BRUSH));
// OK, here is where I tried to tamper with the APIs
// I mentioned earlier
// my goal would be to scale EMF down by half
int prevGraphicsMode = SetGraphicsMode(hdc, GM_ADVANCED);
XFORM zoomMatrix = { 0 };
zoomMatrix.eDx = 0;
zoomMatrix.eDy = 0;
zoomMatrix.eM11 = 0.5;
zoomMatrix.eM12 = 0;
zoomMatrix.eM21 = 0;
zoomMatrix.eM22 = 0.5;
// apply zooming factor
SetWorldTransform(hdc, &zoomMatrix);
// draw image
HENHMETAFILE hemf = GetEnhMetaFile(L".\\Example.emf");
PlayEnhMetaFile(hdc, hemf, &rc);
DeleteEnhMetaFile(hemf);
// restore original graphics mode
SetGraphicsMode(hdc, prevGraphicsMode);
// all done, end painting
EndPaint(hWnd, &ps);
}
return 0L;
In the above snippet, metafile was scaled properly, and was played from the top left corner of the client area.
I didn't bother with maintaining aspect ratio nor centering the image. My main goal for now was to figure out how to use XFORM matrix to scale metafile.
So far so good, at least so I thought.
I tried doing the same as above for the memory device context, but when BitBliting the image I got horrible pixelation, and BitBlitted image was not properly scaled.
Below is the small snippet that reproduces the above image:
static HDC memDC; // in WndProc
static HBITMAP bmp, bmpOld; // // in WndProc; needed for proper cleanup
case WM_CREATE:
{
HDC hdc = GetDC(hwnd);
// create memory device context
memDC = CreateCompatibleDC(hdc);
// get main window's client rectangle
RECT rc = { 0 };
GetClientRect(hwnd, &rc);
// create bitmap that we will draw on
bmp = CreateCompatibleBitmap(hdc, rc.right - rc.left, rc.bottom - rc.top);
// select bitmap into memory device context
bmpOld = (HBITMAP)SelectObject( memDC, bmp );
// fill rectangle with gray brush
FillRect(memDC, &rc, (HBRUSH)GetStockObject(LTGRAY_BRUSH));
// scale EMF down by half
int prevGraphicsMode = SetGraphicsMode(memDC, GM_ADVANCED);
XFORM zoomMatrix = { 0 };
zoomMatrix.eDx = 0;
zoomMatrix.eDy = 0;
zoomMatrix.eM11 = 0.5;
zoomMatrix.eM12 = 0;
zoomMatrix.eM21 = 0;
zoomMatrix.eM22 = 0.5;
// apply zooming factor
SetWorldTransform(memDC, &zoomMatrix);
// draw image
HENHMETAFILE hemf = GetEnhMetaFile(L".\\Example.emf");
PlayEnhMetaFile(memDC, hemf, &rc);
DeleteEnhMetaFile(hemf);
// restore original graphics mode
SetGraphicsMode(memDC, prevGraphicsMode);
// all done end paint
ReleaseDC(hwnd, hdc);
}
return 0L;
case WM_PAINT:
{
PAINTSTRUCT ps;
HDC hdc = BeginPaint(hwnd, &ps);
RECT rc = {0};
GetClientRect(hwnd, &rc);
BitBlt(hdc, 0, 0,
rc.right - rc.left,
rc.bottom - rc.top,
memDC, 0, 0, SRCCOPY);
EndPaint(hwnd, &ps);
}
return 0L;
case WM_DESTROY:
SelectObject(memDC, bmpOld);
DeleteObject(bmp);
DeleteDC(memDC);
PostQuitMessage(0);
break;
After rereading carefully documentation for the BitBlit I have found the following important segment:
If other transformations exist in the source device context (and a matching transformation is not in effect in the destination device context), the rectangle in the destination device context is stretched, compressed, or rotated, as necessary.
Using ModifyWorldTransform(memDC, NULL, MWT_IDENTITY); as user Jonathan Potter suggested fixed this problem.
Those are my tries as far as scaling is concerned. Then I tried to implement scrolling by experimenting with the SetWindowOrgEx and similar APIs.
I have managed to move the image with few experiments, but I haven't fully grasped why and how that worked.
The reason for that is that I was unable to fully understand terms like window and viewport origins and similar. It is just too abstract for me at the moment. As I write this post, I am rereading again and trying to solve this on my own.
QUESTIONS:
How can I use the APIs (from the link I added above) to scale/scroll/scale and scroll metafile in memory DC, and properly BitBlt it in the main window device context?
REMARKS:
I realize that code example could be large, so I do not ask any. I do not want people to write the code for me, but to help me understand what I must do. I just need to fully grasp the concept of applying the above APIs the way I need. Therefore answers/comments can include instructions and small pseudo code, if found appropriate. I realize that the question might be broad, so I would appreciate if you could help me narrow down my problem with constructive criticism and comments.
Thank you for reading this post, offering help, and your understanding.
Best regards.
According to the SetWorldTransform documentation:
it will not be possible to reset the graphics mode for the device
context to the default GM_COMPATIBLE mode, unless the world
transformation has first been reset to the default identity
transformation
So even though you are attempting to reset the graphics mode, with this call:
SetGraphicsMode(memDC, prevGraphicsMode);
This is actually not working, because you are not first resetting the transformation to the identity transform. Adding the following line before the SetGraphicsMode call resets the transform and returns the DC to normal mapping:
ModifyWorldTransform(memDC, NULL, MWT_IDENTITY);
SetGraphicsMode(memDC, prevGraphicsMode);
I would like to do something which I believe is fairly simple but since I am new to the winapi I am finding a lot of problems. Basically I have an HDC (which I am BitBlitting from a loaded Bitmap) and I am drawing a rectangle on it. Then I would like to BitBlt that HDC onto a new HBITMAP Object, but alas for now to no avail.
Here is my code which I have been trying to get to work for a couple of hours now
BITMAPINFO info;
Bitmap *tempbmp = Bitmap::FromFile(L"C:\\Users\\abelajc\\Pictures\\BackgroundImage.png", false);
HBITMAP loadedbackground;
tempbmp->GetHBITMAP(NULL, &loadedbackground);
HBRUSH hRed = CreateSolidBrush(RGB(255, 0, 0));
HDC pDC = GetDC(0);
HDC TmpDC = CreateCompatibleDC(pDC); //main DC on which we will paint on
HDC dcBmp = CreateCompatibleDC(TmpDC); //DC for the loadedbackground HBitmap
HGDIOBJ TmpObj2 = SelectObject(dcBmp , tempbmp); //Selecting Bitmap in DC
BitBlt(TmpDC, 0, 0, 512, 512, dcBmp, 0, 0, SRCCOPY);
SelectObject(dcBmp, TmpObj2); //Deselecting Bitmap from DC
DeleteDC(dcBmp);
RECT rectangle;
SetRect(&rectangle, 5, 5, 20, 20);
FillRect(TmpDC, &rectangle, hRed);
HDC hCompDC = CreateCompatibleDC(TmpDC);
HBITMAP hBmp = CreateCompatibleBitmap(TmpDC, 512, 512);
HBITMAP hOld = (HBITMAP)SelectObject(hCompDC, hBmp);
BitBlt(hCompDC, 0, 0, 512, 512, TmpDC, 0, 0, SRCCOPY);
SelectObject(hCompDC, hOld);
DeleteDC(hCompDC);
Bitmap *image = new Bitmap(hBmp, NULL);
I think you just need some clarification about GDI.
A DC is exactly what its name imply : a device context. It's just a context, nothing concrete. Some DCs are context to a real graphic device, some others (memory DCs) are context to a virtual graphic surface in memory. The DCs you create with CreateCompatibleDC are memory DC, but creating the DC only create the context, not the memory surface. As the MSDN documentation says :
Before an application can use a memory DC for drawing operations, it must select a bitmap of the correct width and height into the DC.
You need to associate a HBITMAP with the DC. After doing that, you can consider that drawing to the DC is essentially drawing to the bitmap. The memory DC is the 'window' to the bitmap.
Once you understand that, you will see that your program can be greatly shortened. Feel free to comment if you still have problems.
I must be doing something wrong or have missed something because all I actually want to is render a rectangle into a bitmap, so that I can CreateWindowEx() on it. Does anyone know what I'm missing?
HDC hdc = GetDC(hWnd);
// Create Pen and brush for the rectangle
HPEN pn = CreatePen(style, stroke, pen);
HBRUSH br = CreateSolidBrush(brush);
// Create a compatible bitmap and DC from the window DC with the correct dimensions
HDC bm_hdc = CreateCompatibleDC(hdc);
HBITMAP hImage = CreateCompatibleBitmap(bm_hdc, sz.x, sz.y);
// Select the bitmap, pen, brush into the DC
HGDIOBJ bm_obj = SelectObject(bm_hdc, hImage);
HGDIOBJ pn_obj = SelectObject(bm_hdc, pn);
HGDIOBJ br_obj = SelectObject(bm_hdc, br);
// Draw the rectangle into the compatible DC with the bitmap selected
::Rectangle(bm_hdc, xPos, yPos, xPos + xSize, yPos + ySize);
// Restore the old selections
SelectObject(bm_hdc, br_obj);
SelectObject(bm_hdc, pn_obj);
SelectObject(bm_hdc, bm_obj);
// Delete the not needed DC, pen and brush
DeleteDC(bm_hdc);
DeleteObject(br);
DeleteObject(pn);
ReleaseDC(hWnd, hdc);
// Create the window and send a message to set the static image
HWND win = CreateWindow(TEXT("STATIC"), NULL, WS_CHILD | SS_BITMAP | WS_VISIBLE, pos.x, pos.y, sz.x, sz.y, hWnd, NULL, hInst, NULL)));
HGDIOBJ obj = (HGDIOBJ)SendMessage(win, STM_SETIMAGE, IMAGE_BITMAP, (LPARAM)hImage);
// Delete the old image
if (obj)
DeleteObject(hImage);
Hummmm... but this doesn't work... All I get is a completely black area and not the rectangle that I have drawn. Any ideas why? Do I need to create another DC and BitBlt() between device contexts?
Thanks for all the help everyone, but I've actually solved it myself and it was SUCH a silly mistake too... Consider this line...:-
::Rectangle(bm_hdc, xPos, yPos, xPos + xSize, yPos + ySize);
Nothing wrong with that at first glance, right? WRONG! If you look at my code, I create a compatible bitmap of the required size to contain my rectangle and try to render the rectangle into this bitmap (which is selected into the DC).
But... WHERE in the bitmap am I rendering? xPos and yPos are window positions of the rectangle, but I'm not rendering to the Window DC am I?!? d'oh! That's right, xPos and yPos should both be 0 because I'm rendering into a bitmap of the correct size and it's when the Window is displayed that xPos and yPos should contain screen coordinates!
Wow... what a dumb mistake and thanks for the nice spot on the HDC from the Window rather than from the compatible DC. I did know that a memory DC has a 1bit depth, but still made that classic blunder. Thanks everyone.
Try changing this line HBITMAP hImage = CreateCompatibleBitmap(bm_hdc, sz.x, sz.y); into this :
HBITMAP hImage = CreateCompatibleBitmap(hdc, sz.x, sz.y);
Paul Watt wrote excellent articles for GDI and image composition with MsImage32.dll.
I am reffering you to this article because it addresses your problem, and here are the relevant quotes and code snippets:
The memory DC is initialized with a mono-chromatic 1x1 pixel bitmap by default.
Avoid a Common Mistake
Before we get too far away from code where I showed you what you need to start running, I want to make sure you are holding this new pair of scissors safely. Do not use a Memory DC with a call to CreateCompatibleBitmap.
...
// You may be tempted to do this; DON'T:
HDC hMemDC = ::CreateCompatibleDC(hDC);
// DON'T DO THIS
// |
// V
HBITMAP hBmp = ::CreateCompatibleBitmap(hMemDC, width, height);
...
// TIP: Try to use the same DC to create
// the Bitmap which you used to create the memory DC.
Remember the part about how The memory DC is initialized with a mono-chromatic 1x1 pixel bitmap by default?!
As for the remarks of member Raymond Chen I believe he is also right, but since you said that your actual code is different this is the only thing I can see as a mistake.
Hopefully this helps.
Best regards.
I'm writing now simple mspaint-like program in C++ using windows.h (GDI). For my program I need only pen tool. So, I need to store somewhere main window's picture (for ex. in memory HDC and HBITMAP) to draw it after in WM_PAINT message.
When I first have to store window's HDC to my memory HDC and HBITMAP? In what message I should store window? For example, I think we can't do it in WM_CREATE because we have no window yet.
What is the difference between PatBlt and BitBlt? What should I use for my app?
How to copy window's HDC content to my memory HDC and Bitmap? I'm trying to do something like this:
LPRECT lpRect;
GetClientRect(hwnd, lpRect);
width = lpRect->right - lpRect->left;
height = lpRect->bottom - lpRect->top;
HDC hDC = GetDC(hwnd);
memoryDC = CreateCompatibleDC(hDC);
memoryBitmap = CreateCompatibleBitmap(hDC, width, height);
SelectObject(memoryDC, memoryBitmap);
PatBlt(memoryDC, 0, 0, width, height, PATCOPY);
ReleaseDC(hwnd, hDC);
But this don't work: program crashes.
How to restore window in WM_PAINT after that?
How to clear my window with white color?
1: I would recommend you lazy load your off-screen canvas as late as possible. If you need it in WM_PAINT and you haven't created it yet, create it then. If you need it at the point someone begins drawing, create it then. If it exists when you need it, then use it.
2: PatBlt fills a region of a bitmap using the device context's current brush. Brushes define patterns, which is why it's called PatBlt. BitBlt copies data from a source bitmap to a destination bitmap. You would use a BitBlt when you wanted to move the image from the off-screen bitmap to the frame buffer.
3: The lpRect parameter of GetClientRect is an output parameter. That means you have to supply the memory. In this case, GetClientRect is trying to write the rectangle to a null pointer and causing the crash.
RECT clientRect;
GetClientRect(hwnd, &clientRect);
width = clientRect.right - clientRect.left;
height = clientRect.bottom - clientRect.top;
WM_PAINT: seems to be the best place to create the memory hdc. You can do something like this
WM_PAINT:
if (!first_paint)
{
...code
first_paint = true;
}
...more code
break;