There is an HBITMAP which can be displayed successfully. I want get a portion (specified by a rect) of the bitmap, so is the following code but the returned bitmap is always black. Is there something wrong with the code? Thanks.
HBITMAP GetSelectedBitmap(HBITMAP p_bitmap, int x, int y, int width, int height){
HDC l_srcDc = ::CreateCompatibleDC(NULL);
::SelectObject(l_srcDc, p_bitmap);
HDC l_dstDc = ::CreateCompatibleDC(l_srcDc);
HBITMAP l_newBitmap = CreateCompatibleBitmap(l_dstDc, width, height);
HBITMAP l_oldBitmap = (HBITMAP)::SelectObject(l_dstDc, l_newBitmap);
ASSERT(0 != ::BitBlt(l_dstDc, 0, 0, width, height, l_srcDc, x, y, SRCCOPY));
HBITMAP l_clippedBitmap = (HBITMAP)::SelectObject(l_dstDc, l_oldBitmap);
::DeleteDC(l_srcDc);
::DeleteDC(l_dstDc);
return l_clippedBitmap;}
I found the cause, change
HBITMAP l_newBitmap = CreateCompatibleBitmap(l_dstDc, width, height);
to
HBITMAP l_newBitmap = CreateCompatibleBitmap(l_srcDc, width, height);
fix the issue. that means CreateCompatibleBitmap should use the source DC.
Related
I am getting a very poor peformance drawing with Win32. It takes too much time and needs improving. Please advise.
Here is what I do.
HDC dc = GetDC(wnd);
HDC memoryDc = CreateCompatibleDC(dc);
HBITMAP memoryMapBitmap = CreateCompatibleBitmap(dc, 400, 400);
HGDIOBJ originalBitmap = SelectObject(memoryDc, memoryMapBitmap);
Then, I draw in a for-loop as follows.
HBRUSH brush = (HBRUSH)GetStockObject(DC_BRUSH);
SetDCBrushColor(memoryDc, colorRef);
FillRect(memoryDc, &rect, brush);
And finally, I do a cleanup
SelectObject(memoryDc, originalBitmap);
DeleteDC(memoryDc);
ReleaseDC(wnd, dc);
Drawing takes a lot of time (several seconds). Is there a way to draw faster with Win32?
Thanks in advance!
It looks like I have solved it. Below is the solution with some comments.
I have a dialog defined in RC-file. There is a control to display a bitmap image in the dialog.
CONTROL "", IDC_MEMORY_MAP, WC_STATIC, SS_BITMAP | SS_CENTERIMAGE | SS_SUNKEN, 9, 21, 271, 338, WS_EX_LEFT
In the run-time I need to create, draw and display a bitmap:
HWND map = GetDlgItem(dlg, IDC_MEMORY_MAP);
HBITMAP bitmap = createMemoryMapBitmap(map);
bitmap = (HBITMAP)SendMessage(map, STM_SETIMAGE, IMAGE_BITMAP, (LPARAM)bitmap);
DeleteObject(bitmap); // (!) this is a very important line, otherwise old bitmap leaks
Code that finds out the size of the bitmap to create:
HBITMAP createMemoryMapBitmap(HWND map) {
RECT rect = {0, 0, 0, 0};
GetClientRect(map, &rect);
SIZE size = {rect.right - rect.left, rect.bottom - rect.top};
HDC dc = GetDC(map);
HBITMAP bitmap = doCreateMemoryMapBitmap(dc, &size);
ReleaseDC(map, dc);
return bitmap;
}
Finally, we actually create the bitmap and draw on it:
HBITMAP doCreateMemoryMapBitmap(HDC dc, LPSIZE bitmapSize) {
// create 24bpp bitmap in memory in order to draw fast
BITMAPINFO info;
memset(&info, 0, sizeof(info));
info.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
info.bmiHeader.biWidth = bitmapSize->cx;
info.bmiHeader.biHeight = bitmapSize->cy;
info.bmiHeader.biPlanes = 1;
info.bmiHeader.biBitCount = 24;
info.bmiHeader.biCompression = BI_RGB;
void *pixels = NULL;
HBITMAP memoryBitmap = CreateDIBSection(dc, &info, DIB_RGB_COLORS, &pixels, NULL, 0);
HDC memoryDc = CreateCompatibleDC(dc); // (!) memoryDc is attached to current thread
HGDIOBJ originalDcBitmap = SelectObject(memoryDc, memoryBitmap);
// drawing code here
// perform windows gdi cleanup
SelectObject(memoryDc, originalDcBitmap); // restore original bitmap in memoryDC (optional step)
DeleteDC(memoryDc); // this releases memoryBitmap from memoryDC
return memoryBitmap;
}
The idea above is to create a 24bpp bitmap in the memory and draw on it. This way drawing is fast, as #IInspectable pointed out.
If display is in the indexed color mode, e.g. 16 or 256 colors, it seems Windows native control is smart enough to convert the color depth automatically displaying the bitmap.
I'm new to win32 and there are some concepts I haven't fully grasped. For one, the difference between HDC and HWND. I understand (or think I understand) that they're handles to a objects and that hdc's can be derived from hwnd's. Like in the case of BeginPaint:
hdc = BeginPaint(hWnd, &ps);
But i don't fully understand what seperates each as certain methods have hdc as parameters and some use hwnd
Secondly, I'm not sure what SelectObject and GetObject do. I think that they associate handles with various objects, like in the case of this bitmap drawing function:
BOOL DrawBitmap (HDC hDC, INT x, INT y, INT width, INT height, HBITMAP hBitmap,
DWORD dwROP)
{
HDC hDCBits;
BITMAP Bitmap;
BOOL bResult;
hDCBits = CreateCompatibleDC(hDC);
GetObject(hBitmap, sizeof(BITMAP), (LPSTR)&Bitmap);
SelectObject(hDCBits, hBitmap);
bResult = StretchBlt(hDC, x, y, width, height,hDCBits, 0, 0, Bitmap.bmWidth,
Bitmap.bmHeight, dwROP);
DeleteDC(hDCBits);
return bResult;
}
But despite all of this I don't understand exactly what they do or how they work. Thanks, in advance.
I have obtained a screenshot by doing the following:
GetDesktopWindow
GetDC
GetClientRect
CreateCompatibleBitmap
This gives me a HBITMAP, I can optionally take it to HDC with:
CreateCompatibleDC
My goal was to end up with a uint8 byte array from either step 4 (CreateCompatibleBitmap) or step 5 (CreateCompatibleDC) is this possible?
Thanks
You need to create a new DC with CreateCompatibleDC(), create a DIB (device-independent bitmap) for this DC with CreateDIBSection(), select the DIB in the new DC with SelectObject(), then copy from your original DC to the new DC with BitBlt(). The pointer retrieved by the CreateDIBSection will point to the raw data. This data is allocated by the system, which means you don't need to allocate it yourself, but it will be freed when you call DeleteObject() for the DIB.
Here is an example in C :
HDC hdcMemoryDC = CreateCompatibleDC(yourDC);
BITMAPINFO bmi;
memset(&bmi, 0, sizeof(BITMAPINFO));
bmi.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
bmi.bmiHeader.biWidth = width;
bmi.bmiHeader.biHeight = -height; // top-down
bmi.bmiHeader.biPlanes = 1;
bmi.bmiHeader.biBitCount = 32;
bmi.bmiHeader.biCompression = BI_RGB;
HBITMAP hbmp;
COLORREF *pixelBuffer;
hbmp = CreateDIBSection( hdcMemoryDC, &bmi, DIB_RGB_COLORS, (VOID**)&pixelBuffer, NULL, 0 );
SelectObject( hdcMemoryDC, hbmp );
BitBlt( hdcMemoryDC, 0, 0, width, height, yourDC, 0, 0, SRCCOPY );
I am trying to capture a screen and assign it to some sort of control so I can click the picture and retrieve the coordinates at which the picture was clicked.
How would I go about doing this? Im trying to assign a bitmap to a static control, and when the user clicks on the image, i retrieve mouse coordinates and subtract the offsetted borders. Im using a static control since it has SS_Notify.
But here the picture isnt even to be able to be displayed on the frame?
What would i do to fix this code?
static HDC handle_MemoryDC;
static HDC handle_ScreenDC;
//BITMAP bitmap;
static HBITMAP handle_Bitmap;
static int x, y;
case WM_CREATE:{
CreateWindowEx(NULL, "STATIC", "", SS_BITMAP|WS_VISIBLE|WS_CHILD, 500,300, 640 ,360 , hwnd, HMENU(IDCSTATIC_BITMAP), GetModuleHandle(NULL), NULL);
handle_ScreenDC = GetDC(NULL);
handle_MemoryDC = CreateCompatibleDC(handle_ScreenDC);
x = GetDeviceCaps(handle_ScreenDC, HORZRES);
y = GetDeviceCaps(handle_ScreenDC, VERTRES);
handle_Bitmap = CreateCompatibleBitmap(handle_ScreenDC, 640, 360);
SelectObject(handle_MemoryDC, handle_Bitmap);
StretchBlt(handle_MemoryDC, 0, 0, 640, 360, handle_ScreenDC, 0, 0, x, y, SRCCOPY);
SendDlgItemMessage(hwnd, IDCSTATIC_BITMAP, STM_SETIMAGE, IMAGE_BITMAP, (LPARAM)handle_Bitmap);
It looks like you are trying to send message to menu (IDCSTATIC_BITMAP), instead of static control. Try to use
SendMessage(hwnd, STM_SETIMAGE, IMAGE_BITMAP, (LPARAM)handle_Bitmap);
Once I have loaded a BITMAP from file, with LoadImage:
HBITMAP renderBMP = (HBITMAP)LoadImage( NULL, filePath, IMAGE_BITMAP, 0, 0, LR_DEFAULTSIZE | LR_LOADFROMFILE );
is there a way to easily access and edit the pixels individually?
I can use this to get the bitmap object, but it doesn't seem to help,
BITMAP bm;
GetObject(renderBMP, sizeof(bm), &bm);
because the value of bmBits in the structure is 0.
UPDATE:
Now I am getting a bug with this solution:
struct Pixel { unsigned char r,g,b,a; };
void Frame::PushMemory(HDC hdc)
{
BITMAPINFO bi;
ZeroMemory(&bi.bmiHeader, sizeof(BITMAPINFOHEADER));
bi.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
GetDIBits(hdc, renderBMP, 0, bi.bmiHeader.biHeight, NULL, &bi, DIB_RGB_COLORS);
/* Allocate memory for bitmap bits */
Pixel* pixels = new Pixel[bi.bmiHeader.biHeight * bi.bmiHeader.biWidth];
int n = sizeof(Pixel) * bi.bmiHeader.biHeight * bi.bmiHeader.biWidth;
int m = bi.bmiHeader.biSizeImage;
GetDIBits(hdc, renderBMP, 0, bi.bmiHeader.biHeight, pixels, &bi, DIB_RGB_COLORS);
// Recompute the output
//ComputeOutput(pixels);
// Push back to windows
//SetDIBits(hdc, renderBMP, 0, bi.bmiHeader.biHeight, pixels, &bi, DIB_RGB_COLORS );
//delete pixels;
}
I get this error:
Run-Time Check Failure #2 - Stack around the variable 'bi' was corrupted.
The last three lines don't seem to matter whether commented in or not.
Use GetDIBits to access pixels. It copies all pixels into specified buffer. After pixels' modification you can use SetDIBits to write pixels back to bitmap.
EDIT:
Example of code:
LPVOID lpvBits=NULL; // pointer to bitmap bits array
BITMAPINFO bi;
ZeroMemory(&bi.bmiHeader, sizeof(BITMAPINFOHEADER));
bi.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
if (!GetDIBits(hDC, hBmp, 0, height, NULL, &bi, DIB_RGB_COLORS))
return NULL;
/* Allocate memory for bitmap bits */
if ((lpvBits = new char[bi.bmiHeader.biSizeImage]) == NULL)
return NULL;
if (!GetDIBits(hDC, hBmp, 0, height, lpvBits, &bi, DIB_RGB_COLORS))
return NULL;
/* do something with bits */
::SetDIBits( hDC, hBmp, 0, height, ( LPVOID )lpvBits, &bi, DIB_RGB_COLORS );
If you pass the LR_CREATEDIBSECTION flag to LoadImage it creates a special kind of bitmap with a usermode memory section containing the bits of the bitmap.
GetObject on a DIBSection bitmap will fill in the bmPits pointer of the BITMAP structure, or even fill in a DIBSECTION struct with extra data.