Thread: Drawing with buttons

ok, i am a newb at drwing in win32 and i did look through the forum for this but didnt really know how to say it so here goes:

i want to be able to have the user click a button that i create and have it draw using setpixel the stuff that i have set up for it but when it do it like this

Code:

case WM_PAINT:
{
    hdc = BeginPaint(hwnd,&ps);
    for(j=0;j<256;j++)
    {
        for(k=0;k<256;k++)
        {
            SetPixel(hdc,j,k,RGB(0,j,k));
        }
    }
    Arc(hdc,100,100,200,200,100,130,100,130);
    EndPaint(hwnd,&ps);
    break;
}
case WM_COMMAND:
{
    switch(LOWORD(wParam))
    {
        case IDC_BUTTON_IMAGE1:
        {
            for(j=0;j<256;j++)
            {
                for(k=0;k<256;k++)
                {
                    SetPixel(hdc,256+j,256+k,RGB(0,j,k));
                }
            }        
            Arc(hdc,200,200,300,300,100,100,200,200);
            break;
        }
    }
    break;
}

only the first part goes, the second part i just get a warning saying

Code:

C:\Documents and Settings\me\Desktop\drawing example\main.cpp(108) : warning C4700: local variable 'hdc' used without having been initialized

I know that i am doing something completely wrong but i do not know what it is?

any help? am i totally lost? i looked in a bunch of tutorials but i couldnt seem to find any help in them...and i dont have the cash to lay out for the book by charles petzold that goes through all the api stuff

any thought?

Code:

case WM_COMMAND:
{
    switch(LOWORD(wParam))
    {
        case IDC_BUTTON_IMAGE1:
        {
            hdc = GetDC(//Handle to window in here//)             
             for(j=0;j<256;j++)
            {
                for(k=0;k<256;k++)
                {
                    SetPixel(hdc,256+j,256+k,RGB(0,j,k));
                }
            }        
            Arc(hdc,200,200,300,300,100,100,200,200);
            break;
        }
    }
    break;

You need to get the device context for your client area before you can draw on it.

GREAT!! thanks, i knew i was forgetting something

Just remember to release it once you are done with it by calling ReleaseDC(). So in your case:

Code:

case WM_COMMAND:
{
    switch(LOWORD(wParam))
    {
        case IDC_BUTTON_IMAGE1:
        {
            hdc = GetDC(/*Handle to window in here*/) ; 
             for(j=0;j<256;j++)
            {
                for(k=0;k<256;k++)
                {
                    SetPixel(hdc,256+j,256+k,RGB(0,j,k));
                }
            }        
            Arc(hdc,200,200,300,300,100,100,200,200);
            ReleaseDC(/*Handle to window in here*/,hdc);
            break;
        }
    }
    break;