collision

[eeyurdakul]

Hi,

I am designing a platform game where objects are .png format using its transparency feature. Is there a function which outputs when two objects collide (I mean when non-transparent parts of  two .png images collide). Could you give me a solution on this?


Thanks

[jamesbowman]

The hardware supports 1-pixel collision detection. You can select an (x, y), then on the next frame the hardware reports what 8-bit tag was drawn at that pixel.

The "frogger" example uses this. It selects the pixel for testing here:

github.com/jamesbowman/gd2-lib/blob/master/frogger.ino#L218

and reads back the result using REG_TAG:

github.com/jamesbowman/gd2-lib/blob/master/frogger.ino#L369

The game draws enemies etc. using GD.Tag(), so for example this draws the cars using tag 2:

github.com/jamesbowman/gd2-lib/blob/master/frogger.ino#L221

J.

[eeyurdakul]

Hi again,

I follow the "frogger" code that you have mentioned, but I have a couple of questions.

Defining two tags; 

GD.Tag(1);
GD.AlphaFunc(GREATER, 0);
GD.Vertex2ii(x, y, SPRITE01_HANDLE, anim);

GD.Tag(2);
GD.AlphaFunc(GREATER, 0);
GD.Vertex2ii(x, y, SPRITE02_HANDLE, anim);

GD.wr(REG_TAG_X, frogx - 8);
GD.wr(REG_TAG_Y, frogy);

then I couldn't get how to compare these two tags.

Could you write a basic example code, it would be great ?

Thanks