Thread: To replace GetPixel(), attemping to use bitmap + pointers to speed things up

Hi everyone!

Getpixel() is too slow so I am trying to use bitmap to load the RGB values into a pointer to access the RGB values rapidly, but it seems
either I messed up on the bitmap operations or I can't get the pointer right!

I use Pixelcolor() to compare so I know I have it right if the returned RGB values matches one another.

Can anyone help me out?

thx!

Code:

#include <iostream>
#include <Windows.h>
using namespace std;

void cout_colour();
void get_pixel();

void main()
{
   cout_colour();
   get_pixel();
}

void cout_colour()
{
   HDC hdc, hdcTemp;
   RECT rect;
   BYTE* bitPointer;

   int red = 0;
   int green = 0;
   int blue = 0;

   hdc = GetDC(GetDesktopWindow());
   GetWindowRect(GetDesktopWindow(), &rect);

   int MAX_WIDTH = rect.right;
   int MAX_HEIGHT = rect.bottom;

   cout << "MAX_WIDTH" << MAX_WIDTH << endl;
   cout << "MAX_HEIGHT" << MAX_HEIGHT << endl;

   hdcTemp = CreateCompatibleDC(hdc);

   BITMAPINFO bitmap;
   bitmap.bmiHeader.biSize = sizeof(bitmap.bmiHeader);
   bitmap.bmiHeader.biWidth = MAX_WIDTH;
   bitmap.bmiHeader.biHeight = MAX_HEIGHT;
   bitmap.bmiHeader.biPlanes = 1;
   bitmap.bmiHeader.biBitCount = 32;
   bitmap.bmiHeader.biCompression = BI_RGB;
   bitmap.bmiHeader.biSizeImage = 0;   
   bitmap.bmiHeader.biClrUsed = 0;
   bitmap.bmiHeader.biClrImportant = 0;


   HBITMAP hBitmap2 = CreateDIBSection(hdcTemp, &bitmap, DIB_RGB_COLORS, (void**)(&bitPointer), NULL, NULL);
   SelectObject(hdcTemp, hBitmap2);
   BitBlt(hdcTemp, 0, 0, MAX_WIDTH, MAX_HEIGHT, hdc, 0, 0, SRCCOPY);


   int i = 1;

   int x = 1;
   int y = 1;
   SetCursorPos(x, y);

   red = (int)bitPointer[i];
   green = (int)bitPointer[i + 1];
   blue = (int)bitPointer[i + 2];

   cout << red << " " << green << " " << blue << endl;

   DeleteDC(hdc);
}

void get_pixel()
{
   int x = 1;
   int y = 1;
   COLORREF hex_color;
   int red;
   int green;
   int blue;
   HDC dc = GetDC(GetDesktopWindow());

   hex_color = GetPixel(dc, x, y);
   red = GetRValue(hex_color);
   green = GetGValue(hex_color);
   blue = GetBValue(hex_color);

   cout << "Super Slow RGB cout!" << endl;
   cout << red << " " << green << " " << blue << endl;
}

got it, thanks!

Note also that the R, G, B values are reversed in a DIBSection.

The least significant byte in 32 bit DIBSection DWORD is blue, not red as it is in a COLORREF value.

You might try using a 32 bit pointer to access the color values in the bitmap. The functions for operating on COLORREF values (eg GetRValue(), RGB(), etc) could be used and are still considerably faster than GetPixel() and SetPixel().