#3487, #3488, #3489, #3490, #3491: Levels (Individual Controls): bound the curve only where it would overflow

The 1e6 bound also capped curves that were finite before (gamma 0.1 on an
HDR value 4 x Input White is 4^10, about 1.05e6). The bound is now 1e30:
1e30 times the widest output range (2e4) is still finite, and every curve
below it renders as before. A test pins 4^10.

crates/effects/src/color2.rs

@@ -257,11 +257,12 @@ impl Lv {
     }
 }
 
-/// How far Levels (Individual Controls)' curve may reach, far beyond any image value: with gamma
-/// down to 0 (rendered as 0.01, an exponent of 100) an HDR value a few times Input White would
-/// overflow `f32`, and an infinite curve times an empty output range is NaN. Bounded, the output
-/// stays finite over the whole valid range (levels ±10000). The GPU (`fxt_lv`) uses the same.
-const LEVELS_IC_CURVE_LIMIT: f32 = 1e6;
+/// How far Levels (Individual Controls)' curve may reach: with gamma down to 0 (rendered as 0.01,
+/// an exponent of 100) an HDR value a few times Input White overflows `f32`, and an infinite curve
+/// times an empty output range is NaN. 1e30 times the widest output range (2e4) is still finite
+/// (`f32::MAX` is 3.4e38), and every curve that was finite before stays as it was below it. The
+/// GPU (`fxt_lv`) uses the same.
+const LEVELS_IC_CURVE_LIMIT: f32 = 1e30;
 
 fn levels_ic(ctx: &EffectCtx, mut b: Buf) -> Buf {
     let lv = LV_IDS.map(|ids| Lv {

crates/effects/src/color2/tests.rs

@@ -294,6 +294,10 @@ fn levels_ic_stays_finite_over_the_whole_range() {
         let out = run("ec.color.levelsic", &img, &lv);
         assert!(out.data.iter().flatten().all(|v| v.is_finite()), "{ib} {iw} {ob} {ow}: {:?}", out.data[0]);
     }
+    // The bound only stops the overflow: an HDR value that was finite before keeps its level
+    // (gamma 0.1 at 4 x Input White: 4^10).
+    let bright = run("ec.color.levelsic", &Image::filled(1, 1, [4.0, 4.0, 4.0, 1.0]), &[("rgb/rgbGamma", num(0.1)), ("clipToOutputWhite", Value::Enum(0))]);
+    assert_eq!(bright.data[0][0], 4.0f32.powf(10.0));
     // Gamma 0 is the limit of a small gamma: below Input White the curve goes to 0.
     let dark = run("ec.color.levelsic", &Image::filled(1, 1, [0.5, 0.5, 0.5, 1.0]), &[("rgb/rgbGamma", num(0.0))]);
     assert!(dark.data[0][0] < 1e-6, "{:?}", dark.data[0]);

crates/gpu/src/shaders/fx_tone.wgsl

@@ -41,7 +41,7 @@ fn fxt_lv(i: u32, v: f32, clip_b: bool, clip_w: bool) -> f32 {
         t = min(t, 1.0);
     }
     // color2::LEVELS_IC_CURVE_LIMIT keeps the curve finite.
-    let curve = clamp(fxt_gamma(t, max(data[o + 2u], 0.01)), -1e6, 1e6);
+    let curve = clamp(fxt_gamma(t, max(data[o + 2u], 0.01)), -1e30, 1e30);
     return data[o + 3u] + (data[o + 4u] - data[o + 3u]) * curve;
 }