Adjustment layers: a Transform replaces the picture below instead of drawing over it (fixes #1524)

crates/render/src/adjustment_tests.rs

@@ -156,6 +156,26 @@ fn motion_and_masks_restrict_the_region() {
     assert!(near(img.get(280, 90), [1.0, 0.0, 0.0], 1e-4));
 }
 
+#[test]
+fn a_transform_replaces_the_picture_below() {
+    // Premiere: Transform on an adjustment layer moves the composite below; it is not a copy
+    // drawn over the untouched original (#1524).
+    let mut s = scene(2);
+    let red = matte(&mut s.p, &mut s.map, [1.0, 0.0, 0.0, 1.0]);
+    place(&mut s.p, s.seq, 0, red);
+    let adj = adjustment(&mut s.p, s.seq, 1);
+    fx(&mut s, adj, "transform");
+    let tf = clip(&mut s, adj).effects.iter_mut().find(|e| e.effect == "transform").unwrap();
+    tf.params.get_mut("scale_height").unwrap().value = ParamValue::Float(50.0);
+    let img = render(&s);
+    assert!(near(img.get(160, 90), [1.0, 0.0, 0.0], 1e-4), "{:?}", img.get(160, 90));
+    assert_eq!(img.get(10, 10), [0.0; 4], "the original is gone outside the scaled picture");
+    // at 50 % opacity: half the original, half the (empty) transformed picture
+    clip(&mut s, adj).effect_mut("opacity").unwrap().params.get_mut("opacity").unwrap().value = ParamValue::Float(50.0);
+    let c = render(&s).get(10, 10);
+    assert!((c[0] - 0.5).abs() < 1e-3 && (c[3] - 0.5).abs() < 1e-3, "{c:?}");
+}
+
 #[test]
 fn nested_adjustment_layers_stay_in_their_sequence() {
     let mut s = scene(2);

crates/render/src/lib.rs

@@ -235,18 +235,27 @@ pub(crate) fn render_seq_tracks(project: &Project, seq: &Sequence, t: Tick, opts
                 mask::apply_effect(&mut adjusted, e, &cx);
             }
             let (op, bl) = opacity_blend(item, mt);
-            // Adjustment layer opacity (and opacity masks, in sequence pixels) mix adjusted over original.
-            let mut out = canvas.snapshot();
-            let mut adj = adjusted;
-            adj.scale_alpha(op);
-            mask::apply_opacity_masks(&mut adj, item, mt, opts.scale);
+            // Adjustment layer opacity (and opacity masks, in sequence pixels) weigh adjusted against original.
+            let mut weight = Image::filled(w, h, [op; 4]);
+            mask::apply_opacity_masks(&mut weight, item, mt, opts.scale);
             // Motion moves / scales the adjustment layer's frame: it only applies inside it.
             if let Some(region) = adjustment_region(seq, item, project, mt, opts.scale, w, h) {
                 let cov: Vec<f32> = region.px.as_chunks::<4>().0.iter().map(|p| p[3]).collect();
+                mask::scale_by(&mut weight, &cov);
+            }
+            let cov: Vec<f32> = weight.px.as_chunks::<4>().0.iter().map(|p| p[3]).collect();
+            let mut out = canvas.snapshot();
+            let mut adj = adjusted;
+            if bl == Blend::Normal {
+                // The adjusted picture replaces the original instead of being drawn over it: what
+                // Transform or Basic 3D leave empty shows nothing of the untransformed picture (#1524).
+                mask::mix(&mut adj, &out, &cov);
+                canvas.set(adj);
+            } else {
                 mask::scale_by(&mut adj, &cov);
+                blend::composite(&mut out, &adj, 1.0, bl);
+                canvas.set(out);
             }
-            blend::composite(&mut out, &adj, 1.0, bl);
-            canvas.set(out);
             continue;
         }
         match item_layer_ex(project, seq, item, t, opts, sources, &tc, true) {