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2d pixel perfect collision detection

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Hey
I can't find any tutorial describing pixel perfect collisions... I would be very grateful for giving any information or links on how to create pixel perfect 2d collision. At least, essential functions to achieve this would be appreciated ^^

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I've found a sample code provided by Evil Steve Here but I can't make it work ;/
I want to set true in CollisionMask1 array for these pixels that are opaque in the rectangle of X: 160 - 240 and Y: 80 - 160
bool* CollisionMask1 = new bool[80 *80];

D3DLOCKED_RECT rct;
RECT rect;
SetRect(&rect, 160, 80, 240, 160);
// Lock the texture to access the pixel data
Input::Obj().Texture->LockRect(0, &rct, &rect, D3DLOCK_READONLY);
// Process the texture, line by line
for(UINT y=0; y<80; ++y)
{
DWORD* pBits = (DWORD*)((BYTE*)rct.pBits + y*rct.Pitch);
for(UINT x=0; x<80; ++x)
{
CollisionMask1[y*80 + x] = (pBits[x]&0xff000000) != 0; // Do whatever here
}
}
if(CollisionMask1[3200]) PostQuitMessage(0); //assuming that the sprite's width and height is 80 pixels the centre of it should be 3200 but program doesn't quit

I would be very grateful for any help and any advise would be mostly appreciated

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Hi,

It looks like you're trying to do the same as i tried on one of my first games.

If i understand you correctly then you want to do collision detection by tracking what color a pixel is on the screen and use this to determine if there has been a collision.

After searching around a lot, i did find something that worked for me.

Fist of all i needed to get a copy of the screen -

if (isfirstrun)
{
backBufferData.Dispose();
backBufferData = new ResolveTexture2D(graphics.GraphicsDevice, graphics.GraphicsDevice.PresentationParameters.BackBufferWidth, graphics.GraphicsDevice.PresentationParameters.BackBufferHeight, 1, graphics.GraphicsDevice.PresentationParameters.BackBufferFormat);
graphics.GraphicsDevice.ResolveBackBuffer(backBufferData);
}

Then determine what the pixel colour is at my collision point -

Color selectedColor3;
Color selectedColor4;

Color[] retrievedColor3;
Color[] retrievedColor4;

GetEnemyCorners(enemypos, enemytexture);
backBufferData.GetData<Color>(0, enemytoprightRectangle, retrievedColor3, 0, 1);
backBufferData.GetData<Color>(0, enemybottomrightRectangle, retrievedColor4, 0, 1);
selectedColor3 = retrievedColor3[0];
selectedColor4 = retrievedColor4[0];
if (selectedColor3 == Color.Red || selectedColor4 == Color.Red || EnemyCross(enemypos, enemytexture))
enemypos -= Vector2.Multiply(enemy1horizontalvelocity, (float)gameTime.ElapsedGameTime.TotalSeconds);


private void GetEnemyCorners(Vector2 enemypos, Texture2D enemy1texture)
{
enemytopleftRectangle = new Rectangle((int)enemypos.X + Goldie.Game1.playerenemyoffset, (int)enemypos.Y, 1, 1);
enemytoprightRectangle = new Rectangle((int)enemypos.X + (Goldie.Game1.enemyframeSize.X-Goldie.Game1.goldframeSize.X), (int)enemypos.Y, 1, 1);
enemybottomrightRectangle = new Rectangle((int)enemypos.X + (Goldie.Game1.enemyframeSize.X - Goldie.Game1.goldframeSize.X), (int)enemypos.Y + Goldie.Game1.goldframeSize.Y, 1, 1);
enemybottomleftRectangle = new Rectangle((int)enemypos.X + Goldie.Game1.playerenemyoffset, (int)enemypos.Y + Goldie.Game1.goldframeSize.Y, 1, 1);

retrievedColor3 = new Color[1];
retrievedColor4 = new Color[1];
}

Then there is the actual collision detection -

if (EnemyCollide(player1pos, enemypos, player1texture, enemytexture))
{
"what you want to do if collision happens."
}

protected bool EnemyCollide(Vector2 player1pos, Vector2 enemypos, Texture2D player1texture, Texture2D enemytexture)
{
player1rect.X = (int)player1pos.X + Goldie.Game1.playerenemyoffset;
player1rect.Y = (int)player1pos.Y;
player1rect.Width = Goldie.Game1.player1frameSize.X - (Goldie.Game1.playerenemyoffset * 2);
enemyrect.X = (int)enemypos.X+Goldie.Game1.playerenemyoffset;
enemyrect.Y = (int)enemypos.Y;
enemyrect.Width = Goldie.Game1.enemyframeSize.X-(Goldie.Game1.playerenemyoffset*2);
enemyrect.Height = enemytexture.Height;

if (enemyrect.Intersects(player1rect))
return true;
else
return false;
}

Now as i said, i'm not expert but this is the starting point i have used.

It may make more sense if you seen the screen shots of my Goldie game at -

[color="#284b72"]http://www.agressive...ure-gallery.php

Ta

Daz

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