Routines
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27781: Check Egg Collision
Used by the routines at Handler_RedBird, Handle_Butterfly, CheckCarEggCollision, HandlerFrog01_CheckEggCollision, Check_Hazard_Collision, Handler_UFO, Handle_Plane_Bomb and Handler_Balloon.
Checks if an egg overlaps with a sprite by comparing their positions. The egg is assumed to be 16 pixels wide and 16 pixels tall, while the target point is offset by 4 pixels in X and 6 pixels in Y to check against the centre of the target sprite.
Input
IX Pointer to sprite data
IY Pointer to egg sprite data
Output
F Carry set = no collision, carry clear = collision
First check horizontal overlap. The egg's centre point (X + 4) is compared against the sprite's horizontal range.
CheckEggCollision 27781 LD A,(IY+0) Load B with the egg's X position (from *IY+0) + 4 (offset to the egg's centre).
27784 ADD A,4
27786 LD B,A
27787 LD A,(IX+0) Load A with the sprite's X position (from *IX+0).
27790 CP B Compare with the egg's centre X position.
27791 CCF Complement the carry flag.
27792 RET C Return if the sprite is to the right of the egg (no overlap; carry is set).
Sprite is to the left so check if its right edge reaches the egg's centre.
27793 ADD A,16 Add 16 to the sprite's X position (add sprite width).
27795 CP B Compare this with the egg's centre X position.
27796 RET C Return (with; carry clear meaning a collision, and carry set meaning no collision).
The two overlap horizontally; now check vertical overlap. The egg's centre point (Y + 6) is compared against the sprite's vertical range.
27797 LD A,(IY+1) Load B with the egg's Y position (from *IY+1) + 6 (offset to the egg's centre).
27800 ADD A,6
27802 LD B,A
27803 LD A,(IX+1) Load A with the sprite's Y position (from *IX+1).
27806 CP B Compare this with the egg's centre Y position.
27807 CCF Complement the carry flag.
27808 RET C Return if the sprite is below the egg (no overlap; carry is set).
Sprite is above so check if its bottom edge reaches the egg's centre.
27809 ADD A,16 Add 16 to the sprite's Y position (add sprite height).
27811 CP B Compare this with the egg's centre Y position.
27812 RET Return (with; carry clear meaning a collision, and carry set meaning no collision).
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