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avm2: Make PerspectiveProjection.focalLength more precise #19748

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merged 2 commits into from
Apr 25, 2025
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avm2: Make PerspectiveProjection.focalLength more precise #19748

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660aa66
avm2: Make PerspectiveProjection.focalLength precise
cookie-s Mar 15, 2025
db5c46c
tests: Use Ruffle approximations in perspective_projection test
cookie-s Mar 15, 2025
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2 changes: 1 addition & 1 deletion core/src/avm2/globals/flash/geom/perspective_projection.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -40,7 +40,7 @@ pub fn get_focal_length<'gc>(
let fov = this.get_slot(pp_slots::FOV).coerce_to_number(activation)?;

let width = get_width(activation, this);
let focal_length = (width / 2.0) / f64::tan(fov / 2.0 * DEG2RAD);
let focal_length = (width / 2.0) as f32 * f64::tan((PI - fov * DEG2RAD) / 2.0) as f32;
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After many trials and observations, I found this code. It doesn't seem to be perfect yet (for edge values like 1e-10), though.

  • 1 / tan x = cot x = tan (pi/2 - x)
  • _ as f32 * f32::tan(_) is not good. This produces better result.

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When we're much closer to FP inaccuracy thresholds, did you also try other tricks like replacing * DEG2RAD by explicit * PI / 180.0? Since doing the multiplication and division separately could also affect the result.

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I tried other cases like _ * PI / 180.0 and _ / 180.0 * PI, and also both Rust std::f64::const::PI and ActionScript Math.PI defined in Math.as, but as far as I tested, they didn't show significant improvement...


Ok(focal_length.into())
}
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35 changes: 11 additions & 24 deletions tests/tests/swfs/avm2/perspective_projection/Test.as
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Original file line number Diff line number Diff line change
Expand Up @@ -50,17 +50,15 @@ package {
for (var i: int = 1; i < 180; i++) {
var pp: PerspectiveProjection = new PerspectiveProjection();
pp.fieldOfView = i;
var fl: Number = pp.focalLength;
trace("FOV to FL", i, roundN(fl, 100)); // FIXME: Large numerical errors
trace("FOV to FL", i, pp.focalLength);
}
}

private function TestFLtoFOV(): void {
for (var i: int = 1; i < 1000; i++) {
var pp: PerspectiveProjection = new PerspectiveProjection();
pp.focalLength = i;
var fl: Number = pp.fieldOfView;
trace("FL to FOV", i, roundN(fl, 100000000000));
trace("FL to FOV", i, pp.fieldOfView);
}
}

Expand Down Expand Up @@ -108,35 +106,34 @@ package {
}

private function TestToMatrix3D(): void {
var precision: Number = 100;
var pp: PerspectiveProjection = new PerspectiveProjection();

trace("// toMatrix3D(default)");
trace(roundVecN(pp.toMatrix3D().rawData, precision));
trace(pp.toMatrix3D().rawData);

trace("// toMatrix3D(FOV: 1)");
pp.fieldOfView = 1;
trace(roundVecN(pp.toMatrix3D().rawData, precision));
trace(pp.toMatrix3D().rawData);

trace("// toMatrix3D(FOV: 100)");
pp.fieldOfView = 100;
trace(roundVecN(pp.toMatrix3D().rawData, precision));
trace(pp.toMatrix3D().rawData);

trace("// toMatrix3D(FOV: 179)");
pp.fieldOfView = 179;
trace(roundVecN(pp.toMatrix3D().rawData, precision));
trace(pp.toMatrix3D().rawData);

trace("// toMatrix3D(FL: 1)");
pp.focalLength = 1;
trace(roundVecN(pp.toMatrix3D().rawData, precision));
trace(pp.toMatrix3D().rawData);

trace("// toMatrix3D(FL: 10)");
pp.focalLength = 10;
trace(roundVecN(pp.toMatrix3D().rawData, precision));
trace(pp.toMatrix3D().rawData);

trace("// toMatrix3D(FL: 10000)");
pp.focalLength = 10000;
trace(roundVecN(pp.toMatrix3D().rawData, precision));
trace(pp.toMatrix3D().rawData);
}

private function TestTransform(): void {
Expand Down Expand Up @@ -179,20 +176,10 @@ package {
private function printProps(pp: PerspectiveProjection): void {
trace(" perspectiveProjection = " + pp);
if (pp) {
trace(" perspectiveProjection.fieldOfView = " + roundN(pp.fieldOfView, 100000000000));
trace(" perspectiveProjection.focalLength = " + roundN(pp.focalLength, 100)); // FIXME: Large numerical errors
trace(" perspectiveProjection.fieldOfView = " + pp.fieldOfView);
trace(" perspectiveProjection.focalLength = " + pp.focalLength);
trace(" perspectiveProjection.projectionCenter = " + pp.projectionCenter);
}
}

private function roundN(n: Number, precision: Number): Number {
return Math.round(n * precision) / precision;
}

private function roundVecN(v: Vector.<Number>, precision: Number): Vector.<Number> {
return v.map(
function (n: Number, _, _): Number {return roundN(n, precision);}
);
}
}
}
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