Switch to precise lerp. (#548)

Reviving #278, fixes #275.

Author: bitshifter

codegen/templates/vec.rs.tera

@@ -1867,7 +1867,7 @@ impl {{ self_t }} {
     #[inline]
     #[must_use]
     pub fn lerp(self, rhs: Self, s: {{ scalar_t }}) -> Self {
-        self + ((rhs - self) * s)
+        self * (1.0 - s) + rhs * s
     }
 
     /// Moves towards `rhs` based on the value `d`.

src/f32/coresimd/vec3a.rs

@@ -726,7 +726,7 @@ impl Vec3A {
     #[inline]
     #[must_use]
     pub fn lerp(self, rhs: Self, s: f32) -> Self {
-        self + ((rhs - self) * s)
+        self * (1.0 - s) + rhs * s
     }
 
     /// Moves towards `rhs` based on the value `d`.

src/f32/coresimd/vec4.rs

@@ -713,7 +713,7 @@ impl Vec4 {
     #[inline]
     #[must_use]
     pub fn lerp(self, rhs: Self, s: f32) -> Self {
-        self + ((rhs - self) * s)
+        self * (1.0 - s) + rhs * s
     }
 
     /// Moves towards `rhs` based on the value `d`.

src/f32/neon/vec3a.rs

@@ -770,7 +770,7 @@ impl Vec3A {
     #[inline]
     #[must_use]
     pub fn lerp(self, rhs: Self, s: f32) -> Self {
-        self + ((rhs - self) * s)
+        self * (1.0 - s) + rhs * s
     }
 
     /// Moves towards `rhs` based on the value `d`.

src/f32/neon/vec4.rs

@@ -747,7 +747,7 @@ impl Vec4 {
     #[inline]
     #[must_use]
     pub fn lerp(self, rhs: Self, s: f32) -> Self {
-        self + ((rhs - self) * s)
+        self * (1.0 - s) + rhs * s
     }
 
     /// Moves towards `rhs` based on the value `d`.

src/f32/scalar/vec3a.rs

@@ -769,7 +769,7 @@ impl Vec3A {
     #[inline]
     #[must_use]
     pub fn lerp(self, rhs: Self, s: f32) -> Self {
-        self + ((rhs - self) * s)
+        self * (1.0 - s) + rhs * s
     }
 
     /// Moves towards `rhs` based on the value `d`.

src/f32/scalar/vec4.rs

@@ -827,7 +827,7 @@ impl Vec4 {
     #[inline]
     #[must_use]
     pub fn lerp(self, rhs: Self, s: f32) -> Self {
-        self + ((rhs - self) * s)
+        self * (1.0 - s) + rhs * s
     }
 
     /// Moves towards `rhs` based on the value `d`.

src/f32/sse2/vec3a.rs

@@ -769,7 +769,7 @@ impl Vec3A {
     #[inline]
     #[must_use]
     pub fn lerp(self, rhs: Self, s: f32) -> Self {
-        self + ((rhs - self) * s)
+        self * (1.0 - s) + rhs * s
     }
 
     /// Moves towards `rhs` based on the value `d`.

src/f32/sse2/vec4.rs

@@ -755,7 +755,7 @@ impl Vec4 {
     #[inline]
     #[must_use]
     pub fn lerp(self, rhs: Self, s: f32) -> Self {
-        self + ((rhs - self) * s)
+        self * (1.0 - s) + rhs * s
     }
 
     /// Moves towards `rhs` based on the value `d`.

src/f32/vec2.rs

@@ -692,7 +692,7 @@ impl Vec2 {
     #[inline]
     #[must_use]
     pub fn lerp(self, rhs: Self, s: f32) -> Self {
-        self + ((rhs - self) * s)
+        self * (1.0 - s) + rhs * s
     }
 
     /// Moves towards `rhs` based on the value `d`.

src/f32/vec3.rs

@@ -759,7 +759,7 @@ impl Vec3 {
     #[inline]
     #[must_use]
     pub fn lerp(self, rhs: Self, s: f32) -> Self {
-        self + ((rhs - self) * s)
+        self * (1.0 - s) + rhs * s
     }
 
     /// Moves towards `rhs` based on the value `d`.

src/f32/wasm32/vec3a.rs

@@ -737,7 +737,7 @@ impl Vec3A {
     #[inline]
     #[must_use]
     pub fn lerp(self, rhs: Self, s: f32) -> Self {
-        self + ((rhs - self) * s)
+        self * (1.0 - s) + rhs * s
     }
 
     /// Moves towards `rhs` based on the value `d`.

src/f32/wasm32/vec4.rs

@@ -730,7 +730,7 @@ impl Vec4 {
     #[inline]
     #[must_use]
     pub fn lerp(self, rhs: Self, s: f32) -> Self {
-        self + ((rhs - self) * s)
+        self * (1.0 - s) + rhs * s
     }
 
     /// Moves towards `rhs` based on the value `d`.

src/f64/dvec2.rs

@@ -692,7 +692,7 @@ impl DVec2 {
     #[inline]
     #[must_use]
     pub fn lerp(self, rhs: Self, s: f64) -> Self {
-        self + ((rhs - self) * s)
+        self * (1.0 - s) + rhs * s
     }
 
     /// Moves towards `rhs` based on the value `d`.

src/f64/dvec3.rs

@@ -759,7 +759,7 @@ impl DVec3 {
     #[inline]
     #[must_use]
     pub fn lerp(self, rhs: Self, s: f64) -> Self {
-        self + ((rhs - self) * s)
+        self * (1.0 - s) + rhs * s
     }
 
     /// Moves towards `rhs` based on the value `d`.

src/f64/dvec4.rs

@@ -816,7 +816,7 @@ impl DVec4 {
     #[inline]
     #[must_use]
     pub fn lerp(self, rhs: Self, s: f64) -> Self {
-        self + ((rhs - self) * s)
+        self * (1.0 - s) + rhs * s
     }
 
     /// Moves towards `rhs` based on the value `d`.

tests/vec2.rs

@@ -843,6 +843,13 @@ macro_rules! impl_vec2_float_tests {
             assert_approx_eq!($vec2::ZERO, v0.lerp(v1, 0.5));
         });
 
+        glam_test!(test_lerp_big_difference, {
+            let v0 = $vec2::new(-1e30, -1e30);
+            let v1 = $vec2::new(16.0, 16.0);
+            assert_approx_eq!(v0, v0.lerp(v1, 0.0));
+            assert_approx_eq!(v1, v0.lerp(v1, 1.0));
+        });
+
         glam_test!(test_move_towards, {
             let v0 = $vec2::new(-1.0, -1.0);
             let v1 = $vec2::new(1.0, 1.0);

tests/vec3.rs

@@ -987,6 +987,13 @@ macro_rules! impl_vec3_float_tests {
             assert_approx_eq!($vec3::ZERO, v0.lerp(v1, 0.5));
         });
 
+        glam_test!(test_lerp_big_difference, {
+            let v0 = $vec3::new(-1e30, -1e30, -1e30);
+            let v1 = $vec3::new(16.0, 16.0, 16.0);
+            assert_approx_eq!(v0, v0.lerp(v1, 0.0));
+            assert_approx_eq!(v1, v0.lerp(v1, 1.0));
+        });
+
         glam_test!(test_move_towards, {
             let v0 = $vec3::new(-1.0, -1.0, -1.0);
             let v1 = $vec3::new(1.0, 1.0, 1.0);

tests/vec4.rs

@@ -1124,6 +1124,13 @@ macro_rules! impl_vec4_float_tests {
             assert_approx_eq!($vec4::ZERO, v0.lerp(v1, 0.5));
         });
 
+        glam_test!(test_lerp_big_difference, {
+            let v0 = $vec4::new(-1e30, -1e30, -1e30, -1e30);
+            let v1 = $vec4::new(16.0, 16.0, 16.0, 16.0);
+            assert_approx_eq!(v0, v0.lerp(v1, 0.0));
+            assert_approx_eq!(v1, v0.lerp(v1, 1.0));
+        });
+
         glam_test!(test_move_towards, {
             let v0 = $vec4::new(-1.0, -1.0, -1.0, -1.0);
             let v1 = $vec4::new(1.0, 1.0, 1.0, 1.0);