Alright, I've been struggling with this for at least a week, time to swallow my pride and ask for help from you clever, clever forum people
I'm trying to make a platform game in Game Maker Studio, and I don't want to use any of the built-in things
(behaviours, drag-and-drop commands, solid flags, etc.) as things are going to get a lot more complicated than they allow.
For now though, I can't even get my collision detection to work.
It seems like the player object gets stuck less-than-a-pixel into walls and floors sometimes. Not all the time, only sometimes, and I really can't tell what causes it, I've changed and re-written this code a bunch of times to try to avoid this, but to no avail.
I've attached my collision detection script, which is called during the end-step of any movable objects (just the player object for now).
The only variables changed by any other code I've written are the player's velX and velY values.
Any help would be seriously appreciated, I'm just banging my head on the keys at this point.
I've also uploaded the
source code, if anybody wants to run the thing (and has GM Studio).
Edit: Haha, ugh, just noticed the horrible spelling in my comments. Take it as a symptom of my frustration.
/*
* THIS IS GOING TO BE COMPLICATED
* use my own x/y/bounds etc values
* read velX and velY from the movable object
*/
//only change velX and velY in the movement scripts, the rest is handeled here.
//get the working bounds
workingLeft = workingX - colWidth/2;
workingRight = workingX + colWidth/2
workingTop = workingY - colHeight/2;
workingBottom = workingY + colHeight/2;
//don't let the player move into walls
if(wallRight && velX > 0){
velX = 0;
}
else if(wallLeft && velX < 0){
velX = 0;
}
if(wallBelow && velY > 0){
velY = 0;
}
else if(wallAbove && velY < 0){
velY = 0;
}
//if the player is moving at all (make this more efficent later)
if(velX != 0 || velY != 0){
//collisions need to be checked along the diagonal line of movement
//SO: get the movement as mag and norms
mag = sqrt(sqr(velX)+sqr(velY));
normX = velX/mag;
normY = velY/mag;
//NOTE: solid objects only have PER PIXEL AABB ACCURACY to their collisions.
//check ahead to find if the obstacle is in our path
maxMag = mag;
maxX = velX;
maxY = velY;
//note: don't check at current position (i=0),
//don't want none of that moving slowly backwards through walls crap
collided = false;
for(i = 1; i < mag; i++){
if(collision_rectangle(workingLeft+normX*i, workingTop+normY*i, workingRight+normX*i, workingBottom+normY*i,
ob_parent_Solid, true, true)){
//at this value of i, the obstacle IS HIT
collided = true;
//therefor, take i-1 dists as MAX NATURAL MOVEMENT DISTANCES
maxX = normX*(i-1);
maxY = normY*(i-1);
break;
}
}
//we might not have to worry about collisions at all
if(!collided){
//just move by velX & velY
workingX += velX;
workingY += velY;
}
//but if we DO have to worry about collisions
if(collided){
//I know that I can DEFINITELY move the ob by maxX & maxY
//but after that movement, at least 1 of the axes will be within a pixel of a collision
//so: round these distances UP and then move
if(velX > 0){
workingX += ceil(maxX);
}
else if(velX < 0){
workingX += floor(maxX);
}
if(velY > 0){
workingY += ceil(maxY);
}
else if(velY < 0){
workingY += floor(maxY);
}
//now I should be RIGHT AT the collision. Perfect.
//just leave things at this for now
}
}
//recheck the walls around the player
if(collision_line(workingLeft-1, workingTop, workingLeft-1, workingBottom, ob_parent_Solid, true, true)){
wallLeft = true
}
else{
wallLeft = false;
}
if(collision_line(workingRight+1, workingTop, workingRight+1, workingBottom, ob_parent_Solid, true, true)){
wallRight = true
}
else{
wallRight = false;
}
if(collision_line(workingLeft, workingTop-1, workingRight, workingTop-1, ob_parent_Solid, true, true)){
wallAbove = true
}
else{
wallAbove = false;
}
if(collision_line(workingLeft, workingBottom+1, workingRight, workingBottom+1, ob_parent_Solid, true, true)){
wallBelow = true
}
else{
wallBelow = false;
}
//finally match x&y to working x&y
x = round(workingX);
y = round(workingY);
Developer
