Calculating collisions with Radians incrementing - trigonometry

Question

While programming a game with the Tululoo Game Maker API, I am having problems with calculating collisions accurately as the x and y are being calculated from the radians.
The calculations for x and y below are producing a large number number of decimal points which I am finding difficult to check for collisions.
image_angle is the final angle of the pistol in degrees that the bullet uses initially.
In Setup:
x = instance_list(pistol)[0].x;
y = instance_list(pistol)[0].y;
startAng = instance_list(pistol)[0].image_angle;
this.travelX = cos(degtorad(instance_list(pistol)[0].image_angle)) * 5;
this.travelY = sin(degtorad(instance_list(pistol)[0].image_angle)) * 5;
In Update Frame:
x+=this.travelX;
y+=this.travelY;
Calculating the Angle that the ball will bounce off a wall at, messy I know:
for(var i = 0; i < instance_number(bounce_barrier);i++){
if(place_meeting(x,y,instance_list(bounce_barrier)[i])){
if(Math.round(x*10)/10 > instance_list(bounce_barrier)[i].x ){
newAng = 180 - startAng;
this.travelX = +cos(degtorad(newAng)) * 15;
this.travelY = +sin(degtorad(newAng)) * 15;
startAng = newAng;
}
else if(y > instance_list(bounce_barrier)[i].y - 5 && y <= instance_list(bounce_barrier)[i].y + 10){
newAng = 180 - startAng;
this.travelX = -cos(degtorad(newAng)) * 15;
this.travelY = -sin(degtorad(newAng)) * 15;
startAng = newAng;
}
else if(y <= instance_list(bounce_barrier)[i].y - 5 + bounce_spr.height && y >= instance_list(bounce_barrier)[i].y + bounce_spr.height - 10){
newAng = 180 - startAng;
this.travelX = -cos(degtorad(newAng)) * 15;
this.travelY = -sin(degtorad(newAng)) * 15;
startAng = newAng;
}
else if(x < instance_list(bounce_barrier)[i].x){
newAng = 180 - startAng;
this.travelX = +cos(degtorad(newAng)) * 15;
this.travelY = +sin(degtorad(newAng)) * 15;
startAng = newAng;
}
else{}
}
}
place_meeting is Part of the Tululoo Game API:
function __place_meeting__(nx, ny, what, many) {
this.other = null;
var i, l,
// sprite, scale:
ts = this.sprite_index,
tsx, tsy, tfx, tfy, tst,
// circle:
tcx, tcy, tcr,
// bbox:
tbl, tbr, tbt, tbb,
// instances, multiple, output, types:
tz, tm, ct, ch, ra,
// other:
o, ox, oy, os, ost, osx, osy, ofx, ofy, ofr;
if (ts == null) return false;
tfx = ts.xoffset;
tfy = ts.yoffset;
tsx = this.image_xscale;
tsy = this.image_yscale;
tst = ts.collision_shape;
// bbox:
if (tst == 2) {
tbl = nx + tsx * (ts.collision_left - tfx);
tbr = nx + tsx * (ts.collision_right - tfx);
tbt = ny + tsy * (ts.collision_top - tfy);
tbb = ny + tsy * (ts.collision_bottom - tfy);
}
// circle:
if (tst == 3) {
tcr = ts.collision_radius * (tsx > tsy ? tsx : tsy);
tcx = nx + tsx * (ts.width / 2 - tfx);
tcy = ny + tsy * (ts.height / 2 - tfy);
}
//
tz = (what.__instance ? [what] : instance_list(what));
tm = many ? true : false;
if (tm) ra = [];
l = tz.length;
for (i = 0; i < l; i++) {
o = tz[i];
if (!o.collision_checking) continue;
os = o.sprite_index;
if (os == null) continue;
ox = o.x; osx = o.image_xscale;
oy = o.y; osy = o.image_yscale;
ost = os.collision_shape;
ct = (tst << 4) | ost;
ch = false;
switch(ct) {
case 0x22:
if (osx == 1 && osy == 1) {
ofx = os.xoffset; ofy = os.yoffset;
if (!collide_bbox_bbox(tbl, tbt, tbr, tbb,
ox + os.collision_left - ofx, oy + os.collision_top - ofy,
ox + os.collision_right - ofx, oy + os.collision_bottom - ofy)) break;
} else if (!collide_bbox_sbox(tbl, tbt, tbr, tbb, ox, oy, osx, osy, os)) break;
ch = true;
break;
case 0x23:
ofr = os.collision_radius * (osx > osy ? osx : osy);
ofx = ox + osx * (os.width / 2 - os.xoffset);
ofy = oy + osy * (os.height / 2 - os.yoffset);
if (!collide_bbox_circle(tbl, tbt, tbr, tbb, ofx, ofy, ofr)) break;
ch = true;
break;
case 0x32:
if (osx == 1 && osy == 1) {
ofx = os.xoffset; ofy = os.yoffset;
if (!collide_bbox_circle(
ox + os.collision_left - ofx, oy + os.collision_top - ofy,
ox + os.collision_right - ofx, oy + os.collision_bottom - ofy,
tcx, tcy, tcr)) break;
} else if (!collide_sbox_circle(ox, oy, osx, osy, os, tcx, tcy, tcr)) break;
ch = true;
break;
case 0x33:
ofr = os.collision_radius * (osx > osy ? osx : osy);
ofx = ox + osx * (os.width / 2 - os.xoffset);
ofy = oy + osy * (os.height / 2 - os.yoffset);
if (!collide_circle_circle(tcx, tcy, tcr, ofx, ofy, ofr)) break;
ch = true;
break;
} if (!ch) continue;
this.other = o;
o.other = this;
if (!tm) return (o);
ra.push(o);
} return ra;
}
I have managed to make a bullet bounce off a wall at an angle proportional to where it has been shot from, but the collision detection is very bad as it bounces some bullets but not all, some just go straight through the wall.
Just added the Line Collision Detection, ive made the bullets lines so I can see the
this.oldTravelX,this.oldTravelY to this.travelX,this.travelY. It has definitely improved but some of the bullets are still going through.
Some bullets seem to stick inside the bouncing block or slide down the left side of the bouncing block then decide whether to go left or right.
Updated Code:
pntdis = point_distance(this.oldTravelX, this.oldTravelY, this.travelX, this.travelY);
noPoints = pntdis/0.01;
for(var i=0; i < pntdis; i+=noPoints)
{
pointsArrX[i] = this.travelX - (this.oldTravelX * i);
pointsArrY[i] = this.travelY - (this.oldTravelY * i);
}
for(var i=0;i<pointsArrX.length;i++){
if(place_meeting(Math.round(pointsArrX[i]),Math.round(pointsArrY[i]),bounce_barrier) || place_meeting(x,y,bounce_barrier))
{
newAng = 180 - startAng;
this.travelX = +cos(degtorad(newAng)) * 15;
this.travelY = +sin(degtorad(newAng)) * 15;
startAng = newAng;
}
}
Thanks in advance.

Answer 1

It looks like the place_meeting function is supposed to determine whether there's a collision between the bullet and the barrier. However, this function only takes the new position of the bullet. Given the bullet moves 5 units per update, it's possible that the bullet could move from one side of the barrier to the other in a single frame. e.g.:
|
. |
\| barrier
\
|\_______
\
.
place_meeting should take both the old and new positions of the bullet so that it can determine whether any intermediate position collided with the barrier (e.g. by doing line-line intersection testing with the path of the bullet and the edges of the barrier; it should probably also return the collision point).
EDIT
Your updated code looks like it's intended to check for collision of a number of points along the path of the bullet. There are faster ways to do this, but your method may be fast enough, and is easy to understand. There appears to be a bug in how you calculate the points to check though.
Stepping through the code manually on paper:
pntdis = 5 // assume point_distance returns 5
noPoints = 5 / 0.01 = 500
i = 0
pointsArrX[0] = this.travelX
pointsArrY[0] = this.travelY
i = i + noPoints = 500
500 < 5: false, for loop ends
Other things to consider:
You might want a break statement after you've detected a collision so you don't keep testing further points.
You could combine the two for loops into one because you're not reusing the values in the array. Just calculate your test point and then test it immediately.
Try using console.log to output debugging information as your program runs so you can get a better idea of what's happening.
Use var before your variables (such as pntdis and noPoints) to avoid accidentally creating global variables.