Math for perfect collision - Help?

[Captain Spazer]

I'm struggling with my math and I could use a little help:

The player collides with pfpixel, pfpixel gets turned off, but the collision detection is wonky. The player sprite is 8x8.
 

 x = (player0x-18)/4 : y = (player0y)/8
 x = (player0x-18)/4 : y = (player0y)/8
 if collision(playfield,player0) then pfpixel x y off

Entire code:
 

 rem Generated 30/01/2020 19:42:08 by Visual bB Version 1.0.0.554
 rem **********************************
 rem *<filename>                      *
 rem *<description>                   *
 rem *<author>                        *
 rem *<contact info>                  *
 rem *<license>                       *
 rem **********************************

start

 set smartbranching on

 dim rand16 = z

 dim _P0_L_R = player0x.k
 dim _P0_U_D = player0y.l

 a = 10
 player0x = 50
 player0y = 10


 rem FIX THIS CODE! MAKE IT SPAWN 10 PFPIXELS:
Loop_Lettuce
 d = 0
Place_Lettuce

 temp1 = (rand&31)
 temp2 = (rand&7) - 1
 pfpixel temp1 temp2 flip
 d = d +1
 if d = 10 then goto main
 goto Place_Lettuce

main

 COLUP0=$0E
 COLUP1=$33

 COLUBK=$D8
 COLUPF= $DC

 rem PLAYER0 Bunny
 if a = 10 then player0:
 %00110100
 %00111100
 %01111100
 %00111110
 %00011101
 %00000110
 %00000100
 %00000100
end

 if a = 20 then player0:
 %00110000
 %00100000
 %00011010
 %00111100
 %00011110
 %00001101
 %00000010
 %00001100
end

 if a = 30 then player0:
 %00000100
 %00001100
 %00011110
 %00111101
 %01110110
 %10100100
 %00001000
 %00000000
end

 if a > 30 then a = 0

 rem flip p0 sprite
 if c = 0 then REFP0=0
 if c = 1 then REFP0=8

 drawscreen
 rem ANIMATE AND MOVE BUNNY
 if joy0up then _P0_U_D = _P0_U_D - 0.50 : a = a + 1
 if joy0down then _P0_U_D = _P0_U_D + 0.50 : a = a + 1
 if joy0left then _P0_L_R = _P0_L_R - 0.50 :  a = a + 1 : c = 1
 if joy0right then _P0_L_R = _P0_L_R + 0.50 :  a = a + 1 : c = 0
 if !joy0left && !joy0right && !joy0up && !joy0down then a = 10

 rem BUNNY EATS LETTUCE
 x = (player0x-18)/4 : y = (player0y)/8
 x = (player0x-18)/4 : y = (player0y)/8

 if collision(playfield,player0) then pfpixel x y off

 goto main

 

Edited January 31, 2020 by Captain Spazer
More info

[+Random Terrain]

The numbers are slightly different depending on which direction you move. Make a test program where you turn on pixels, play with the numbers until they are perfect, then use those numbers in your program.

[Captain Spazer]

Ahh, that was very hard, but I got it working now that I understood that the direction of movement mattered.

[Captain Spazer]

While on the subject of math, how would I go about looping the spawn of the pfpixels for example 10 times?

My current code seems to be wonky, sometimes I get 8 pfpixels, sometimes 9 and sometimes 10:

 

Loop_Lettuce
 d = 0
Place_Lettuce

 temp1 = (rand&31)
 temp2 = (rand&14) - 1
 pfpixel temp1 temp2 on
 d = d +1
 if d >= 10 then goto main
 goto Place_Lettuce

 

[+Random Terrain]

You could check for a pfpixel using pfread so you never plop on top of a pixel that is already there.