How does bitmaps draw pixel on window?

Question

So I followed a few tutorials on how to draw on window using windows.h library, the part of the tutorial that I don't really understand is the bitmap part. They used createbitmap() and StrechBit() functions to draw on window. Do window references bitmap to draw pixels on the screen accordingly and bitmap is basically a chunk of memory large enough to store pixel's position and color value. If so, does bitmap automatically generate every time you created a window, because it seems that you don't really need to declare bitmap or use createbitmap() functions to type word on the window you created, you only need to create bitmap when you want to draw a custom pixel.

Answer 1

A window will receive the WM_PAINT message when it needs to be painted. This can happen because InvalidateRect was called, the window was resized etc.

Where the pixels are stored ("in" the HWND) is an implementation detail you don't have to worry about. On some versions/configurations the GDI functions are hardware accelerated and the result might be stored directly in the GPU, in others everything might be implemented in software and run on the CPU. When using a layered window I'm guessing everything older than Vista will use an internal bitmap to store the pixels.

GDI/GDI+ is the classic way to draw windows. If you need per-pixel alpha transparency you would draw to a bitmap and call UpdateLayeredWindow , otherwise you would just draw using any GDI function you want in WM_PAINT . This might include drawing one or several bitmaps, text, and lines/curves directly to the HWNDs HDC. As this can cause flicker in certain cases (if any area is drawn to more than once in one paint cycle), so people might draw to their own bitmap first and then BitBlt this bitmap to the window, this is called double-buffering.

The new way to draw is Direct2d/ DirectComposition .