Routines
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CD33: Calculate Sprite Size
Used by the routine at FlagOverlappingObjects.
Works out where an object is on the screen and how much of the screen its sprite covers. The width in bytes is one more than the width of the sprite if the sprite does not start on a byte boundary, because it has to be shifted across.
Input
IX Address of the object
Work out the pixel position, then the width and height of the sprite.
CalculateSpriteSize CD33 CALL CalculatePixelCoordinates Work out the pixel coordinates of the object.
CD36 CALL GetSpriteAddress Find the sprite of the object, and flip it if it needs it.
CD39 LD A,(IX+$1A) Fetch the pixel X coordinate.
CD3C AND %00000111 Keep the offset of the bit within the byte.
CD3E LD A,(DE) Fetch the width of the sprite in bytes.
CD3F INC DE Point DE at the height of the sprite.
CD40 JR Z,CalculateSpriteSize_Store Jump to CalculateSpriteSize_Store if the sprite starts on a byte boundary.
CD42 INC A Add one byte to the width.
CalculateSpriteSize_Store CD43 AND %00001111 Keep the low nibble of the width.
CD45 LD (IX+$18),A Store the width in bytes.
CD48 LD A,(DE) Fetch the height of the sprite in lines.
CD49 LD (IX+$19),A Store the height in lines.
CD4C RET Return.
View the equivalent code in;
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