Keystone warp issue.

alex.ep

in Contributed Library Questions • 16 days ago

I'm trying to create a program that will straighten a trapezium into a square (as you do). The program is supposed to use it's knowledge of the shape of the trapezium to then apply a transformation to the cornerPins to straighten the shape out. I can roughly do it by mouse manually but this is unacceptable as a final result due to many issues: mainly accuracy and speed. These images should help demonstrate what I'm trying to do.

* *First image is original shape before the warp, in the second image the green trapezium has become a square from the warp.**

Ultimately I'm looking for either a formula or function that will allow me to find how much to raise/lower the cornerpins to straighten the square.

Current code:

import deadpixel.keystone.*;
Keystone ks;
CornerPinSurface surface;
MeshPoint pnt;
PGraphics offscreen;
void setup() {
size(1280, 720, P3D);
smooth();
ks = new Keystone(this);
surface = ks.createCornerPinSurface(400, 400, 20);
offscreen = createGraphics(400, 400, P3D);
}
void draw() {
offscreen.beginDraw();
offscreen.background(255);
offscreen.fill(#67cd47);
offscreen.strokeWeight(2);
offscreen.beginShape();
offscreen.vertex(0, 50);
offscreen.vertex(400, 0);
offscreen.vertex(400, 400);
offscreen.vertex(0, 400-150);
offscreen.endShape(CLOSE);
offscreen.endDraw();
background(80);
surface.render(offscreen);
}
void keyPressed() {
switch (key) {
case 'c':
ks.toggleCalibration();
break;
case 't':
println(CornerPinSurface.BR);
surface.moveMeshPointBy(surface.BL, 0.0, 10.0); //The amout '10.0' needs to be replaced by the amount to move down.
break;
}
}

Replies(2)

kooogy

Re: Keystone warp issue.

16 days ago

let's try this

you effectively have a line:

a---b---c---d
which you want to change to
a---b-----------c----d

so, using a linear equation
f(x) = nx + m;

f(b) = a;
f(c) = d;

nb + m = a
nc + m = d

take second away from first to remove m gives

n = (a - d) / (b -c)

substituting into the first
b ((a - d) / (b - c)) + m = a

so m = a - bn

something like that. probably easier when you have real numbers to use.

ok, say a = 4, b = 6, c = 8, d = 10
n = (4-10) / (6 - 8) = 3, so stretch the line by a factor of 3
which gives a = 12, b = 18, c = 24, d = 30
you'll notice the the distance between b and c is now 6, the same as the distance between the original a and d.
m = a - 3b = 4 - 18 = -14. so shift all the values by -14 giving
a = -2, b = 4, c = 10, d = 16
new b is the old value of a (4), new c is the old value of d (10)

(edit: fixed first of probably many errors)
(edit: real numbers example)

kooogy

Re: Keystone warp issue.

16 days ago

or, in words, you need to stretch the line so that the two middle points are separated by the same distance as the distance between the two other dots (the n) and then move the line so that they line up (the m).

(i'll try and put the above into code tonight, might be easier)

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