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nodes: pivot transform rotation/scale around the frame center

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The transform shader sampled in a top-left-origin pixel space while
Olive's transform semantics (and every other node) are center-origin:
rotation swung the image around the top-left corner, pushing it partly
off-frame - reading exactly like an unwanted zoom. Match the C++
transform.vert projection: position (0,0) is the frame center and
rotation/scale pivot around the anchor, so rotation and scale stay
independent user controls. GPU tests pin the 90-degree landing spot
(no smearing) and the 2x scale centroid (stays centered).
This commit is contained in:
Mike-Solar
2026-09-10 18:13:05 +08:00
parent 280118a342
commit d028a45ffa
2 changed files with 89 additions and 5 deletions
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crates/oak-node/src/nodes/transformdistortnode.rs
+9 -5
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@@ -24,9 +24,12 @@
/// The transform fragment shader: samples the input through the inverse
/// of the node's pixel-space transform (`transform_in` carries the
/// CPU-inverted matrix; `resolution_in` is auto-filled by the runner).
/// The C++ path transforms vertices (`ove_mvpmat` in transform.vert);
/// an affine transform is equivalently applied fragment-side by
/// inverse-mapping the sample position — the fixed fullscreen vertex
/// Pixel space is CENTER-origin (C++ `transform.vert` transforms the
/// quad in the frame-centered projection): position (0,0) is the frame
/// center and rotation/scale pivot around the anchor — NOT around the
/// top-left corner, which is what a top-left-origin pixel space would
/// pivot on (a corner pivot swings the image off-frame as it rotates,
/// reading exactly like an unwanted zoom). The fixed fullscreen vertex
/// stage stays unchanged.
const TRANSFORM_FRAG: &str = r#"uniform sampler2D tex_in;
uniform mat4 transform_in;
@@ -36,8 +39,9 @@ in vec2 ove_texcoord;
out vec4 frag_color;
void main(void) {
vec2 px = ove_texcoord * resolution_in;
vec2 src = (transform_in * vec4(px, 0.0, 1.0)).xy;
vec2 half_res = resolution_in * 0.5;
vec2 px = ove_texcoord * resolution_in - half_res;
vec2 src = (transform_in * vec4(px, 0.0, 1.0)).xy + half_res;
frag_color = texture(tex_in, src / resolution_in);
}
"#;