L_PaintDCBufferCallback

Summary

Paints image data from a buffer using paint callbacks.

Syntax

#include "l_bitmap.h"

L_LTDIS_API L_INT L_PaintDCBufferCallback(pCallbackData, pBitmap, pSrc, pSrcClip, pDest, pDestClip, uROP3, pBuffer, nBufferRow, nNumRows)

Parameters

pPAINTCALLBACKDATA pCallbackData

Pointer to a structure containing the device context (DC) and the paint callbacks. The mapping mode of the device context must be MM_TEXT.

pBITMAPHANDLE pBitmap

Pointer to the bitmap handle that describes the image to paint.

L_RECT * pSrc

Pointer to the Windows RECT structure that specifies the part of the bitmap to use as the display source.

The coordinates in the RECT structure are relative to the bitmap. You can pass NULL to use the default, which matches the bitmap.

L_RECT * pSrcClip

Pointer to the Windows RECT structure that specifies the portion of the display source to paint. Generally, this is used for updating the display when part of the source bitmap has changed.

The coordinates in the RECT structure are relative to the bitmap. You can pass NULL to use the default, which matches the bitmap.

L_RECT * pDest

Pointer to the Windows RECT structure that determines how the source rectangle is scaled and how the image is positioned in the device context.

The coordinates in the RECT structure are relative to the device context. There is no default for this parameter. You must specify the RECT structure.

L_RECT * pDestClip

Pointer to the Windows RECT structure that specifies the portion of the display rectangle to paint. Generally, this is used for updating changes in the display surface, such as when a user moves another window, uncovering a part of the image that had been covered up.

The coordinates in the RECT structure are relative to the device context. You can pass NULL to use the default, which matches the device context. In most cases, however, you should use the rectangle returned by the Windows WM_PAINT message.

L_UINT32 uROP3

The Windows ROP code that determines how the destination rectangle is updated. This parameter takes the same codes as the Windows BitBlt function. For ordinary painting, use SRCCOPY.

L_UCHAR * pBuffer

Pointer to the buffer that contains the image data to paint.

L_INT nBufferRow

The first row to paint. The painted portion of any row may be limited by the RECT parameters.

L_INT nNumRows

The number of rows to paint. The painted portion of any row may be limited by the RECT parameters. If the image data in pBuffer is compressed 1-bit data, you can specify the number of lines as a negative value (-nLines), as explained in Speeding Up 1-Bit Documents.

Returns

Value	Meaning
SUCCESS	The function was successful.
< 1	An error occurred. Refer to Return Codes.

Comments

The HDC you are painting to should stored in the PAINTCALLBACKDATA structure. Refer to its documentation for details on which GDI functions you can override.

This function references a LEAD bitmap handle, which may or may not have a loaded bitmap. In either case, the following fields must be specified in the BITMAPHANDLE structure:

The Width, Height, BitsPerPixel, Order, and ViewPerspective fields must all be set to the correct values for the image. (You can use the L_InitBitmap function to set the values.)
The pPalette must be a valid palette (an array of RGBQUAD values). You can create or update the palette using the L_PutBitmapColors function.

Except for the buffer specifications, this function uses source and destination rectangles the same as L_PaintDC. For a complete explanation, refer to L_PaintDC.

You can call L_PaintDCBufferCallback from a callback function to paint an image while a bitmap is being loaded. This technique is used in the FILEREADCALLBACK procedures in the DEMO.C example program.

Required DLLs and Libraries

LTDIS
For a listing of the exact DLLs and Libraries needed, based on the toolkit version, refer to Files To Be Included With Your Application.

Platforms

Win32, x64.

Example

Gets the data one line at a time and paints it.

L_INT PaintDCBufferExample(L_HWND hWnd, pBITMAPHANDLE pBitmap) 
{ 
   L_INT             nRet = SUCCESS; 
   HDC               hdc;                    /* Device context for the current window */ 
   RECT              rcDest;                 /* Destination rectangle for painting */ 
   HPALETTE          hSavedPalette = NULL;   /* Temporary copy of the current system palette */ 
   HPALETTE          hOurPalette = NULL;     /* The palette that we will use to paint */ 
   L_INT             x; 
   PAINTCALLBACKDATA PaintCallbackData;      /* Paint callback data structure */ 
 
   /* Get the device context */ 
   hdc = GetDC(hWnd); 
 
   /* Set the destination rectangle to be the same as the bitmap. 
   Other painting rectangles can take defaults. */ 
   GetClientRect(hWnd, &rcDest); 
 
   /* Create the palette that we will use to paint */ 
   hOurPalette = L_CreatePaintPalette(hdc, pBitmap); 
 
   /* Select our palette and save the old one */ 
   hSavedPalette = SelectPalette(hdc, hOurPalette, FALSE); 
 
   /* Realize our palette */ 
   RealizePalette(hdc); 
 
   /* Initialize the paint callback data structure */ 
   memset(&PaintCallbackData, 0, sizeof(PaintCallbackData)); 
   PaintCallbackData.uStructSize = sizeof(PAINTCALLBACKDATA); 
   PaintCallbackData.pDisplay = hdc; 
 
   /* set the paint callbacks for the GDI functions you are overriding here 
 
        PaintCallbackData.pIsCompatibleDC = MyIsCompatibleDC; 
        PaintCallbackData.pStretchDIBits = MyStretchDIBits; 
        etc 
   */ 
 
   /* Paint the image */ 
   nRet = L_AccessBitmap(pBitmap); 
   if (nRet != SUCCESS) 
      return nRet; 
 
   for (x = 0; x < pBitmap->Height; x++) 
   { 
      L_UCHAR* pBuf = (L_UCHAR*)malloc(pBitmap->BytesPerLine); 
      nRet = (L_INT)L_GetBitmapRow(pBitmap, pBuf, x, pBitmap->BytesPerLine); 
      if (nRet < 1) 
         return nRet; 
 
      nRet = L_PaintDCBufferCallback(&PaintCallbackData, pBitmap, NULL, NULL, &rcDest, NULL, SRCCOPY, pBuf, x, 1); 
      if (nRet < SUCCESS) 
         return nRet; 
   } 
 
   L_ReleaseBitmap(pBitmap); 
 
   /* Restore the old palette */ 
   SelectPalette(hdc, hSavedPalette, FALSE); 
 
   /* Delete the newly created palette */ 
   DeleteObject(hOurPalette); 
 
   /* Release the device context */ 
   ReleaseDC(hWnd, hdc); 
 
   return nRet; 
}