Drawing issues with c++

Question

I'm sort of new to c++ and i'm trying to create a game. I have a 2d array RECT_GRID of rectangles. I have a 2d array GRID of unsigned short. I fill the rectangle array during WM_CREATE

The WM_PAINT event paints rectangles for all the elements in the array. The color of the rectangle is based on the value of GRID[x][y]

I made it so when the down key is pressed, It changes the color of one of the rectangles by setting GRID[1][XMOVE] = to a different color then it invalidates the client rectangle

Basically what happens is, it works well for a while, but eventually it just stops drawing stuff. I checked my XMOVE variable during debug, I checked by grid values and stuff and everything is fine. When I remove the for loop from the paint event and focus on 1 specific rectangle, it never fails, but if I try to redraw all of them at once, after about 20 times, it stops painting things. What could cause this? I'm new to c++ and I bet I'm not painting properly and causing an overflow or something.

If anyone could explain what's going wrong, or a proper way to do this, I'd really appreciate it. I could not find anything like this example on Google. Thanks

EDIT:

I'm using 3 global brushes HBRUSH A; HBRUSH B; HBRUSH C;

and when I modify them, I always say A = MakeBrush(NUM);

ami I using brushes properly?

Answer 1

My first guess, if you're a total GDI/C++ newbie, is that you are probably creating a lot of Pens and Brushes. These are constrained resources in Windows. You can only create so many of them before you start to tax your resources. So either make your Brushes and Pens and Windows, etc all at once and re-use them, or dispose of them properly when you're done. I recommend getting a copy of "the Bible" (http://www.amazon.com/Programming-Windows%C2%AE-Fifth-Microsoft/dp/157231995X/ref=sr_1_1?ie=UTF8&s=books&qid=1252788457&sr=8-1) and reading the chapters in there about drawing.

EDIT: It doesn't sound like you're modifying your brushes properly, but since I can't see the code for MakeBrush, I don't know. You're probably creating a lot of brushes behind the scenes and you don't even know it. Seriously, get a copy of Petzold's book and spend an hour or two. You'll end up with more hair on your head later! ;-)

Answer 2

You'll notice in all GDI examples, a 'CreatePen' or 'CreateSolidBrush' will be followed by a delete object. This is because they are limited resources in windows, and you can run out of them if you don't delete them when you're finished.

PAINTSTRUCT Ps;
HDC hDC = BeginPaint(hWnd, &Ps);
HBRUSH NewBrush = CreateSolidBrush(RGB(250, 25, 5));

SelectObject(hDC, NewBrush);
Rectangle(hDC, 20, 20, 250, 125);
DeleteObject(NewBrush);
EndPaint(hWnd, &Ps);

If you forget to include the 'DeleteObject' call, then you will have problems after you use up all the brushes available. It's actually fun to try =)