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Member Since 02 Sep 2007
Offline Last Active Mar 02 2013 06:36 AM

Topics I've Started

2D isometric picking problem

03 December 2012 - 12:57 AM

Hello all, I have a problem with my 2D isometric picking.
I've asked on gamedev.stackexchange too, but so far I have no answer. You can read the stackexchange question here. It contains details. I will write a short version here.

Here's the code I have for drawing the tiles
// Draw code
int col = 0;
int row = 0;
for (int i = 0; i < nrOfTiles; ++i)
	// XOffset and YOffset are currently hardcoded values, but will represent camera offset combined with HUD offset
	Point tile = IsoToScreen(col, row, TileWidth / 2, TileHeight / 2, XOffset, YOffset);
	int x = tile.X;
	int y = tile.Y;
	spriteBatch.Draw(_tiles[i], new Rectangle(tile.X, tile.Y, TileWidth, TileHeight), Color.White);
	if (col >= Columns) // Columns is the number of tiles in a single row
		col = 0;
// Get selection overlay location (removed check if selection exists for simplicity sake)
Point tile = IsoToScreen(_selectedTile.X, _selectedTile.Y, TileWidth / 2, TileHeight / 2, XOffset, YOffset);
spriteBatch.Draw(_selectionTexture, new Rectangle(tile.X, tile.Y, TileWidth, TileHeight), Color.White);
// End of draw code
public Point IsoToScreen(int isoX, int isoY, int widthHalf, int heightHalf, int xOffset, int yOffset)
	Point newPoint = new Point();
	newPoint.X = widthHalf * (isoX + isoY) + xOffset;
	newPoint.Y = heightHalf * (-isoX + isoY) + yOffset;
	return newPoint;

And here is the code for getting which tile is the mouse on
public Point? ScreenToIso(int screenX, int screenY, int tileHeight, int offsetX, int offsetY)
	Point? newPoint = null;
	int nX = -1;
	int nY = -1;
	int tX = screenX - offsetX;
	int tY = screenY - offsetY;
	nX = -(tY - tX / 2) / tileHeight;
	nY = (tY + tX / 2) / tileHeight;
	newPoint = new Point(nX, nY);
	return newPoint;

This code is close, but not even close enough for a public beta or something like that (even though this is just a proof of concept, which I will later transform into my game). I have no idea why this code is so close. I drew the tiles by thinking up the formula, and by googling I believe I've seen that it is correct (however it's still possible it's not). The code for picking - what ever I came up with, didn't work. What ever I googled, didn't work. This code I currently have is a derivation of something I googled - it was not really close, but closer than others, so I modified it and it's even closer now - I did it by trial and error as I have no idea behaved and behaves the way it did/does.

Can anyone point out to me my error? Whenever I think about it, it doesn't make sense to me that it behaves that way. I tried reversing the formula for drawing and it didn't pan out which doesn't make sense either. I must be doing something wrong then so please, if someone sees my error, could you point it out?

Get pixel color with GetBitmapBits

02 September 2007 - 08:44 PM

Hi! I am a begginer in C++ builder, but I have started working on a plugin and I did manage to make some cool functions, but I have GetPixel and SetPixel too, which would be awesome if it weren't so slow... Btw, I am using only WinAPI functions to make the plugin much smaller (from aprox. 50 kb to aprox. 10 kb) so I would like it to stay that way... I was stumped with how to fix this so I asked how to fix this, what to do and I got this answer:
   HDC hDC,                  // Handle to the display device context
   hDCMem;               // Handle to the memory device context
   HBITMAP hBitmap;          // Handle to the new bitmap
   int iWidth, iHeight;      // Width and height of the bitmap
   int iDoneBits;	    // Changed bits
   int bitColorARRAY_SIZE;   // Size of the array
   int *bitColorARRAY_PTR;   // Pointer to the array with pixels
   // Retrieve the handle to a display device context for the client
   // area of the window.
   hDC = GetDC (hwnd);

   // Create a memory device context compatible with the device.
   hDCMem = CreateCompatibleDC (hDC);

   // Retrieve the width and height of window display elements.
   iWidth = GetSystemMetrics (SM_CXSCREEN) / 10;
   iHeight = GetSystemMetrics (SM_CYSCREEN) / 10;

   // Create a bitmap compatible with the device associated with the
   // device context.
   hBitmap = CreateCompatibleBitmap (hDC, iWidth, iHeight);

    iDoneBits = SetBitmapBits(hBitmap, bitColorARRAY_SIZE, bitColorARRAY_PTR)

// Insert code to use the bitmap.

   // Delete the bitmap object and free all resources associated with it.
   DeleteObject (hBitmap);

   // Delete the memory device context and the display device context.
   DeleteDC (hDCMem);
   DeleteDC (hDC);
I couldn't figure out this code completly... I have tried to implement it, but never succesfully... I understand some parts of the code, while I don't understand others... Some parts I understand, but I don't know how the code should look exactly... So could someone please explain some things to me? Why is iWidth and iHeight /10 and not just the function return value? Where do I use the MemoryDC? What I need to do with it? I know something about the lines need to be aligned and stuff, but I just can't seem to get it from everything I read on the net... So if someone would be please be so kind to try and explain this stuff a bit to me... How would I get a string in format "R,G,B" from an exact pixel... So let's say I want to get the color of the pixel on the screen with coordinates 20,53 and I need to get this in a string like "255,238,13"... How would I set a pixel like that? I am sorry I can't understand this code and I bug you, but for some reason I just can't seem to figure this code out... Thanx!