CODEWITHSUNDEEP
c++winapibitmap
Arseniy
Arseniy

Reputation: 304

How to store multiple bitmaps in a class?

I want to create a class that generates some bitmaps at runtime and then draws them in the context of the target device on request.

I try this:

myBitmaps.h

#include <windows.h>

class myBitmaps 
{ 
public:
  void myBitmaps(HDC hDC);
  const int size = 16;
  HDC firstDC; 
  HBITMAP firstBuff;
  HDC secondDC; 
  HBITMAP secondBuff;

  void drawBitmap(HDC hDC, int xPos, int yPos, bool first);
}

myBitmaps.cpp

#include "myBitmaps.h"

void myBitmaps(HDC hDC)
{
  firstDC = CreateCompatibleDC(hDC); 
  firstBuff = CreateCompatibleBitmap(hDC, size, size); 
  SelectObject(firstDC, firstBuff);
  ...draw some lines...
  secondDC = CreateCompatibleDC(hDC); 
  secondBuff = CreateCompatibleBitmap(hDC, size, size); 
  SelectObject(secondDC, secondBuff);
  ...draw some lines...
}

void drawBitmap(HDC hDC, int xPos, int yPos, bool first)
{
  if(first) {
    BitBlt(hDC, xPos, yPos, size, size, firstDC , 0, 0, SRCCOPY);
  }
  else {
    BitBlt(hDC, xPos, yPos, size, size, secondDC , 0, 0, SRCCOPY);
  }  
}

But this code causes a runtime error.

How can I store multiple bitmaps in my class?

Upvotes: 0

Views: 142

Answers (1)

Strive Sun
Strive Sun

Reputation: 6299

There can be only one type of each GDI object selected into any type of DC at a time. The memory DC is unique, because it is the only type of DC that is possible to use an HBITMAP with a call to ::SelectObject. Unlike other GDI object types, the HBITMAP can only be selected into one DC at a time. Therefore, if you are using the same bitmap with multiple memory DCs, be sure to save the original HGDIOBJ pushed-out from the memory DC when you select your bitmap into the DC. Otherwise, your attempt to select the bitmap into a second memory DC will fail.

For more details, please refer to the link below.

Guide to Win32 Memory DC

The link lists a lot of things you should pay attention to when using CompatibleDC in the link. Please read them carefully.

Upvotes: 2

Related Questions