[RESOLVED] Difficulty Plotting Pixels

[jroeser]

I'm having difficulty plotting pixels on a black window. I'm using Visual C++ 6.0, and seem can't seem to figure out why my program won't plot these pixels. Basically, I use a for loop to plot roughly a 1000 pixels each with a different color. Here is my code:

#define WIN32_LEAN_AND_MEAN

#include <windows.h>
#include <windowsx.h>
#include <stdio.h>
#include <stdlib.h>
#include <math.h>

//defines
#define WINDOW_CLASS_NAME "WINCLASSONE"

//some globals here

//WindosProc
LRESULT CALLBACK WindowProc(HWND hwnd, UINT msg, WPARAM wparam, LPARAM lparam)
{
	PAINTSTRUCT ps;
	HDC hdc;

	//handle our messages now
	switch(msg)
	{
		case WM_CREATE:
			{
				return(0);
			} break;

		case WM_PAINT:
			{
				hdc = BeginPaint(hwnd, &ps);
				EndPaint(hwnd, &ps);
				return(0);
			} break;

		case WM_DESTROY:
			{
				PostQuitMessage(0);
				return(0);
			} break;

		default: break;

	}

	//as for any of the other messages we didn't get....
	return (DefWindowProc(hwnd, msg, wparam, lparam));
}

//WinMain here
int WINAPI WinMain(HINSTANCE hinstance, HINSTANCE hprevinstance, LPSTR lpcmdline, int ncmdshow)
{
	WNDCLASSEX winclass1;
	HWND hwnd; //generic window handle
	MSG msg; //generic message

	winclass1.cbSize = sizeof(WNDCLASSEX);
	winclass1.style = CS_DBLCLKS | CS_OWNDC | CS_HREDRAW | CS_VREDRAW;

	winclass1.lpfnWndProc = WindowProc;
	winclass1.cbClsExtra = 0;
	winclass1.cbWndExtra = 0;
	winclass1.hInstance = hinstance;
	winclass1.hIcon = LoadIcon(NULL, IDI_APPLICATION);
	winclass1.hCursor = LoadCursor(NULL, IDC_ARROW);
	winclass1.hbrBackground = (HBRUSH)GetStockObject(BLACK_BRUSH);
	winclass1.lpszMenuName = NULL;
	winclass1.lpszClassName = WINDOW_CLASS_NAME;
	winclass1.hIconSm = LoadIcon(NULL, IDI_APPLICATION);

	if (!RegisterClassEx(&winclass1))
		return(0);

	if (!(hwnd = CreateWindowEx(NULL, WINDOW_CLASS_NAME, "A Window",
		WS_OVERLAPPEDWINDOW | WS_VISIBLE,
		0,0,
		400,400,
		NULL,
		NULL,
		hinstance,
		NULL)))
		return(0);


	while(GetMessage(&msg, NULL, 0, 0))
	{
		TranslateMessage(&msg);
		DispatchMessage(&msg);
	}

	//pixel practice
	HDC hdc;
	hdc=GetDC(hwnd);
	for (int index=0; index < 1000; index++)
	{
		int x = rand()%400;
		int y = rand()%400;

		COLORREF color = RGB(rand()%255, rand()%255, rand()%255);
		SetPixel(hdc, x, y, color);
	}
	ReleaseDC(hwnd, hdc);


	return(msg.wParam);
}

I suspect that it is something to do with the the whole GetDC/ReleaseDC/BeginPaint/EndPaint deal, but I'm not sure where the error lies. My program compiles without any errors as well! I know that I'm not even close to understanding the Windows API as well as I should be, but I hope to get better with it through practice. I greatly appreciate any help in advance!

[hoxsiew]

Whoa there. You should be doing your painting in the message loop (WM_PAINT), not AFTER the message loop exits!.

[jroeser]

Doh! Don't I feel stupid! Thank you, I cut and pasted my code into WM_PAINT and it worked right away. I'm still getting a feel for how this Windows stuff works. Thanks for the help!

[hoxsiew]

Also, note that the WM_PAINT section already has a DC for you to paint on. You can eliminate some of your code and just use the paint DC. Always do all your painting between the BeginPaint() and EndPaint().