Implement a function which checks whether two sprites are undergoing pixel-level collision. Rather than bounding box collision in which the containing rectangles overlap, pixel level collision occurs when (and only when) one or more opaque elements of the sprites occupy the same location in the screen frame of reference.

#include #include #include #include #include #include #include #include #include

// (Task 1) Define a function called pixel_level_collision which detects whether // two sprites s1 and s2 collide at pixel level. The function must be able // to work correctly even if the ZDK screen has not been set up, and should // make no attempt to use any function or variable declared in // , either directly or indirectly. // // Parameters: // s1 - the address of a Sprite which has been initialised and placed at // arbitrary position on the screen. // // s2 - the address of a Sprite which has been initialised and placed at // arbitrary position on the screen. // // Returns: // A boolean value which is true if and only if there exists a point (x,y) // which is opaque in both s1 and s2. // // Definition: (x,y) is opaque in sprite s if and only if: // 0 <= (sx = x - round(s->x)) < s->width, and // 0 <= (sy = y - round(s->y)) < s->height, and // offset(s,x,y) = sy * s->width + sx, and // s->bitmap[offset(s,x,y)] != ' '.

INSERT RETURN_TYPE FUNCTION_NAME ( PARAMETER_LIST ) { INSERT CODE HERE }

char * cross = "y y" /**/ " y y " /**/ " y " /**/ " y y " /**/ "y y" ; char * plus = " z " /**/ " z " /**/ "zzzzz" /**/ " z " /**/ " z " ;

int main( void ) { setup_screen(); sprite_id s_cross = sprite_create( 20.9, 8.3, 5, 5, cross ); sprite_id s_plus = sprite_create( 30.9, 17.9, 5, 5, plus );

while ( true ) { clear_screen(); sprite_draw( s_cross ); sprite_draw( s_plus ); if ( pixel_level_collision( s_cross, s_plus ) ) { draw_string(0, 0, "Pixel-level collision has been detected!"); } show_screen();

int key = wait_char();

if ( key == '2' ) { s_plus->y++; } else if ( key == '8' ) { s_plus->y--; } else if ( key == '4' ) { s_plus->x--; } else if ( key == '6' ) { s_plus->x++; } else if ( key == 'q' ) { break; } }

cleanup_screen();

return 0; }

Things to avoid

Do not attempt to draw the sprites within pixel_level_collision. This will cause bad things to happen.