Why does the line equation hate me so?

[RedRogueXIII]

Here is my test platform code for a 2d sidescroller, handling slopes and such, I've gotten the main char ( a red ball ) to land on the platform then ascend a steep slope without weird bouncing, but on a slightly inverted 30* and less it gives me this weird bouncing. on straight surfaces it works fine.

code:

View.Set ("graphics:max,max, offscreenonly") var x1, y1, x2, y2, meX, meY, distance : int var m, b : real var tX, tY : int var controls : array char of boolean % The line works fine on a straight or steep slope but screws up on a small slope x1 := 200 y1 := 300 x2 := 500 y2 := 400 meX := 300 meY := 400 fcn wallDETECTION (x1_, y1_, x2_, y2_, charX_, charY_ : int, m_, b_ : real) : boolean     var x, y, ratio : real     var angle : int     for i : x1_ .. x2_         x := i         y := (m_ * x) + b_         drawdot (round (x), round (y), black)         /*if (charX_ - round (x)) not= 0 then          ratio := (charY_ - round (y)) / (charX_ - round (x))          else          ratio := (charY_ - round (y)) / 0.001          end if          angle := round (arctand (abs (ratio)))          if (charX_ - round (x)) < 0 then          angle := 180 - angle          end if          if (charY_ - round (y)) < 0 then          angle := 360 - angle          end if          locate (1, 1)          put angle ..*/         if Math.Distance (x, y, charX_, charY_) <= 5 then %and angle >= 0 and angle <= 180 then             %if angle = 27 or angle = 180 then             %    meY += 5             %end if             %put "HIT:" ..             result true         end if     end for     result false end wallDETECTION proc initialize (x1_, y1_, x2_, y2_ : int)     x1 := x1_     x2 := x2_     y1 := y1_     y2 := y2_     if x2 - x1 <= 0 then         m := (y2 - y1) / 0.0000001     else         m := (y2 - y1) / (x2 - x1)     end if     b := (m * x1 - y1) * -1     distance := round (sqrt ((x2 - x1) ** 2 + (y2 - y1) ** 2)) end initialize proc move     Input.KeyDown (controls) % PROBLEM AREA     % The t variables represents the line and the balls position shifted up by 5     % The me variables is the ball shifted up 5, cept that it descends down into the t's trajectory.     if controls (KEY_RIGHT_ARROW) then         if wallDETECTION (x1, y1, x2, y2, meX, meY, m, b) = true then             meX += 5             tX := meX             meY := round ((m * intreal (meX)) + b) + 5             tY := round ((m * intreal (meX)) + b)         else             meX += 5         end if     elsif controls (KEY_LEFT_ARROW) then         if wallDETECTION (x1, y1, x2, y2, meX, meY, m, b) = true then             meX -= 5             tX := meX             meY := round ((m * intreal (meX)) + b) + 5             tY := round ((m * intreal (meX)) + b)         else             meX -= 5         end if     end if     if controls (KEY_UP_ARROW) then         meY += 10     end if     if wallDETECTION (x1, y1, x2, y2, meX, meY, m, b) = false then         meY -= 5         tX := meX         tY := meY     end if end move initialize (x1, y1, x2, y2) loop     move     View.Update     cls     drawline (x1, y1, x2, y2, black)     drawoval (meX, meY, 5, 5, red)     drawoval (meX, meY - 5, 5, 5, 1)     drawoval (tX, tY, 5, 5, green)     delay (10)     locate (1, 1)     put meX, " ", meY ..     locate (2, 1)     put meX, " ", meY - 5 .. end loop % Need to check for Steep slopes and change so that movement falls better :D

Can anyone help me debug this annoying glitch?

[Cervantes]

I had a similar question a while back. I don't think I ever solved it, but the code there might be of some use. Not sure.

[NikG]

I think your problem lies in the fact that whenever the left or right arrow is pressed and there is a collision, you are added 5 to meX (and doing whatever to the other variables).

Instead, you should have your move function make your ball move 5 pixels in the direction of the slope. Something along the lines of:

code:

meX += 5 * cosd(angle) meY += 5 * sind(angle)

where angle is the angle of the line segment the ball is on...

I think that should stop the bouncing effect.

[NikG]

Sorry for the double post, I just thought I'd test out what I suggested:

code:

View.Set ("offscreenonly") var chars : array char of boolean var meX, meY := 100.0 var angle := 30 loop     Input.KeyDown (chars)     if chars (KEY_RIGHT_ARROW) then         meX += 5 * cosd (angle)         meY += 5 * sind (angle)     elsif chars (KEY_LEFT_ARROW) then         meX -= 5 * cosd (angle)         meY -= 5 * sind (angle)     end if     drawoval (round (meX), round (meY), 5, 5, black)     View.Update     delay (25)     cls end loop

angle represents the angle of the line segment the ball is on. Try changing it and running the program; the ball moves pretty smoothly at every angle I believe.

The only problem I see with the approach is that if you have a vertical angle (say 80-90 degrees), the ball moves up/down when you press right/left, but you can probably limit this easily.