Pixel Collision

[johnno56]

I figured that I might try some 'old school' collision detection...

The concept is... A falling box. An area to land on. Using the 'pixel()' command, instruct the box to stop, as it "hits" the ground.

In this example, I am testing the pixel below the box's left bottom edge. (I have placed a reference pixel under the box at the same "y" co-ordinate.)

Press SPACE to drop...

Code:

' Open a window and enable double buffering.
set window "Pixel Collision", 640, 480
set redraw off

visible Box = [255, 255, 0, 64]
visible BoxW = 32
visible BoxH = 48
visible BoxX = (width(primary) - BoxW) / 2
visible BoxY = 0
visible vSpeed = 0
visible drop = false

visible ground = [0, 255, 0]

do

    set color 0, 0, 0
    cls
   
    Update()
    Draw()
   
    redraw
    fwait 30
   
until keydown(KEY_ESCAPE, true)

function Update()
    '   vSpeed
    if keydown(KEY_SPACE, true)     drop = true
    if drop = true  vSpeed = vSpeed + 0.03
   
    '   Box
    BoxY = BoxY + vSpeed
   
    '   Pixel Collision
    if pixel(BoxX, BoxY + BoxH) = ground
        vSpeed = 0
    endif
   
    '   Just in case 'pixel' fails... lol
    if BoxY > height(primary)
        vSpeed = 0
        wait 1000
        end
    endif
endfunc

function Draw()
    '   Ground
    set color ground
    draw rect 0, 460, 640, 20, 0
   
    '   Box
    set color Box
    draw rect BoxX, BoxY, BoxW, BoxH, 0
   
    '   Pixel
   
    '   This indicator pixel is drawn one pixel below the box center.
    '   The actual pixel being tested is below the left corner of the box.
    set color 255, 0, 255
    draw pixel BoxX + 15, BoxY + BoxH
endfunc

Unfortunately this did not work... "Read the manual", I hear you say... "pixel(x,y) Returns the color at position (x, y) as an array [r, g, b, a] with RGBA intensities in the range [0 .. 255].

I am hoping that my programing skills are the source of the problem otherwise this maybe another "can of worms".... sorry...