diff --git a/shared/build.rs b/shared/build.rs
index 104c9d6..de7e557 100644
--- a/shared/build.rs
+++ b/shared/build.rs
@@ -2,4 +2,13 @@ fn main() {
     // This allows "spirv" to be used in #[cfg(target_arch = "...")]
     // without triggering a warning.
     println!("cargo:rustc-check-cfg=cfg(target_arch, values(\"spirv\"))");
+
+    // `gpu` is set for every device backend, so host-only code can be gated once
+    // as #[cfg(not(gpu))] instead of naming each target. Adding a backend means
+    // editing this line, not 30-odd cfg attributes.
+    println!("cargo::rustc-check-cfg=cfg(gpu)");
+    let target = std::env::var("TARGET").unwrap_or_default();
+    if target.contains("spirv") || target.contains("cuda") {
+        println!("cargo::rustc-cfg=gpu");
+    }
 }
diff --git a/shared/src/cameras/orthographic.rs b/shared/src/cameras/orthographic.rs
index 021d549..98f42e0 100644
--- a/shared/src/cameras/orthographic.rs
+++ b/shared/src/cameras/orthographic.rs
@@ -24,7 +24,7 @@ pub struct OrthographicCamera {
     pub dy_camera: Vector3f,
 }
 
-#[cfg(not(target_os = "cuda"))]
+#[cfg(not(gpu))]
 impl OrthographicCamera {
     pub fn new(
         base: CameraBase,
diff --git a/shared/src/cameras/perspective.rs b/shared/src/cameras/perspective.rs
index e6ced0c..644d95b 100644
--- a/shared/src/cameras/perspective.rs
+++ b/shared/src/cameras/perspective.rs
@@ -26,7 +26,7 @@ pub struct PerspectiveCamera {
     pub cos_total_width: Float,
 }
 
-#[cfg(not(target_os = "cuda"))]
+#[cfg(not(gpu))]
 impl PerspectiveCamera {
     pub fn new(
         base: CameraBase,
diff --git a/shared/src/core/camera.rs b/shared/src/core/camera.rs
index 12dd9f9..6066c22 100644
--- a/shared/src/core/camera.rs
+++ b/shared/src/core/camera.rs
@@ -137,7 +137,7 @@ pub trait CameraTrait {
     fn generate_ray(&self, sample: CameraSample, lambda: &SampledWavelengths) -> Option<CameraRay>;
 
     fn get_film(&self) -> &Film {
-        #[cfg(not(target_os = "cuda"))]
+        #[cfg(not(gpu))]
         {
             if self.base().film.is_null() {
                 panic!(
diff --git a/shared/src/core/film.rs b/shared/src/core/film.rs
index a0c7283..258f326 100644
--- a/shared/src/core/film.rs
+++ b/shared/src/core/film.rs
@@ -96,7 +96,7 @@ impl RGBFilm {
     }
 
     pub fn get_sensor(&self) -> &PixelSensor {
-        #[cfg(not(target_os = "cuda"))]
+        #[cfg(not(gpu))]
         {
             if self.base.sensor.is_null() {
                 panic!(
@@ -203,7 +203,7 @@ impl RGBFilm {
 
 #[repr(C)]
 #[derive(Debug, Clone)]
-#[cfg_attr(target_os = "cuda", derive(Copy))]
+#[cfg_attr(gpu, derive(Copy))]
 pub struct GBufferPixel {
     pub rgb_sum: [AtomicFloat; 3],
     pub weight_sum: AtomicFloat,
@@ -240,7 +240,7 @@ impl Default for GBufferPixel {
 
 #[repr(C)]
 #[derive(Debug, Clone)]
-#[cfg_attr(target_os = "cuda", derive(Copy))]
+#[cfg_attr(gpu, derive(Copy))]
 pub struct GBufferFilm {
     pub base: FilmBase,
     pub output_from_render: AnimatedTransform,
@@ -294,7 +294,7 @@ impl GBufferFilm {
     }
 
     pub fn get_sensor(&self) -> &PixelSensor {
-        #[cfg(not(target_os = "cuda"))]
+        #[cfg(not(gpu))]
         {
             if self.base.sensor.is_null() {
                 panic!(
@@ -387,7 +387,7 @@ impl GBufferFilm {
 
 #[repr(C)]
 #[derive(Debug)]
-#[cfg_attr(target_os = "cuda", derive(Copy))]
+#[cfg_attr(gpu, derive(Copy))]
 pub struct SpectralPixel {
     pub rgb_sum: [AtomicFloat; 3],
     pub rgb_weight_sum: AtomicFloat,
@@ -419,7 +419,7 @@ impl Default for SpectralPixel {
 
 #[repr(C)]
 #[derive(Debug)]
-#[cfg_attr(target_os = "cuda", derive(Copy, Clone))]
+#[cfg_attr(gpu, derive(Copy, Clone))]
 pub struct SpectralFilm {
     pub base: FilmBase,
     pub lambda_min: Float,
@@ -609,7 +609,7 @@ pub struct FilmBase {
 
 #[repr(C)]
 #[derive(Debug)]
-#[cfg_attr(target_os = "cuda", derive(Copy, Clone))]
+#[cfg_attr(gpu, derive(Copy, Clone))]
 pub enum Film {
     RGB(RGBFilm),
     GBuffer(GBufferFilm),
diff --git a/shared/src/core/interaction.rs b/shared/src/core/interaction.rs
index 7cffc05..6efe884 100644
--- a/shared/src/core/interaction.rs
+++ b/shared/src/core/interaction.rs
@@ -590,7 +590,7 @@ impl SurfaceInteraction {
         }
     }
 
-    #[cfg(not(target_os = "cuda"))]
+    #[cfg(not(gpu))]
     pub fn set_intersection_properties(
         &mut self,
         mtl: MaterialIdx,
diff --git a/shared/src/core/light.rs b/shared/src/core/light.rs
index ca71193..8e9136a 100644
--- a/shared/src/core/light.rs
+++ b/shared/src/core/light.rs
@@ -61,7 +61,7 @@ pub struct LightLiSample {
     pub p_light: Interaction,
 }
 
-#[cfg(not(target_os = "cuda"))]
+#[cfg(not(gpu))]
 impl LightLiSample {
     pub fn new(l: SampledSpectrum, wi: Vector3f, pdf: Float, p_light: Interaction) -> Self {
         Self {
@@ -188,7 +188,7 @@ pub struct LightBounds {
     pub two_sided: bool,
 }
 
-#[cfg(not(target_os = "cuda"))]
+#[cfg(not(gpu))]
 impl LightBounds {
     pub fn new(
         bounds: &Bounds3f,
@@ -327,13 +327,13 @@ pub trait LightTrait {
         self.base().light_type
     }
 
-    #[cfg(not(target_os = "cuda"))]
+    #[cfg(not(gpu))]
     fn bounds(&self) -> Option<LightBounds>;
 
-    #[cfg(not(target_os = "cuda"))]
+    #[cfg(not(gpu))]
     fn preprocess(&mut self, scene_bounds: &Bounds3f);
 
-    #[cfg(not(target_os = "cuda"))]
+    #[cfg(not(gpu))]
     fn phi(&self, lambda: SampledWavelengths) -> SampledSpectrum;
 }
 
diff --git a/shared/src/core/medium.rs b/shared/src/core/medium.rs
index 7727821..79d6e7a 100644
--- a/shared/src/core/medium.rs
+++ b/shared/src/core/medium.rs
@@ -99,7 +99,7 @@ pub struct MajorantGrid {
 
 
 impl MajorantGrid {
-    #[cfg(not(target_os = "cuda"))]
+    #[cfg(not(gpu))]
     pub fn new(bounds: Bounds3f, res: Point3i) -> Self {
         let n_voxels = (res.x() * res.y() * res.z()) as usize;
         let voxels = gvec_with_capacity(n_voxels);
diff --git a/shared/src/core/texture.rs b/shared/src/core/texture.rs
index 4aacb05..df97b88 100644
--- a/shared/src/core/texture.rs
+++ b/shared/src/core/texture.rs
@@ -245,7 +245,7 @@ pub struct PointTransformMapping {
 }
 
 impl PointTransformMapping {
-    #[cfg(not(target_os = "cuda"))]
+    #[cfg(not(gpu))]
     pub fn new(texture_from_render: Transform) -> Self {
         Self {
             texture_from_render,
diff --git a/shared/src/lights/diffuse.rs b/shared/src/lights/diffuse.rs
index 4532af9..bf09729 100644
--- a/shared/src/lights/diffuse.rs
+++ b/shared/src/lights/diffuse.rs
@@ -130,7 +130,7 @@ impl LightTrait for DiffuseAreaLight {
         }
     }
 
-    #[cfg(not(target_os = "cuda"))]
+    #[cfg(not(gpu))]
     fn phi(&self, lambda: SampledWavelengths) -> SampledSpectrum {
         let mut l = SampledSpectrum::new(0.);
         if !self.image.is_null() {
@@ -153,10 +153,10 @@ impl LightTrait for DiffuseAreaLight {
         PI * two_side * self.area * l
     }
 
-    #[cfg(not(target_os = "cuda"))]
+    #[cfg(not(gpu))]
     fn preprocess(&mut self, _scene_bounds: &Bounds3f) {}
 
-    #[cfg(not(target_os = "cuda"))]
+    #[cfg(not(gpu))]
     fn bounds(&self) -> Option<LightBounds> {
         let mut phi = 0.;
         if !self.image.is_null() {
diff --git a/shared/src/lights/goniometric.rs b/shared/src/lights/goniometric.rs
index 9881f31..607dd7f 100644
--- a/shared/src/lights/goniometric.rs
+++ b/shared/src/lights/goniometric.rs
@@ -1,5 +1,8 @@
-use crate::core::geometry::{Bounds3f, Normal3f, Point2f, Point2i, Point3f, Ray, Vector3f};
+use crate::core::geometry::{
+    Bounds3f, Normal3f, Point2f, Point2i, Point3f, Ray, Vector3f, VectorLike,
+};
 use crate::core::image::Image;
+use crate::core::interaction::{Interaction, InteractionBase, SimpleInteraction};
 use crate::core::light::{
     LightBase, LightBounds, LightLiSample, LightSampleContext, LightTrait, LightType,
 };
@@ -34,12 +37,20 @@ impl LightTrait for GoniometricLight {
 
     fn sample_li(
         &self,
-        _ctx: &LightSampleContext,
+        ctx: &LightSampleContext,
         _u: Point2f,
-        _lambda: &SampledWavelengths,
+        lambda: &SampledWavelengths,
         _allow_incomplete_pdf: bool,
     ) -> Option<LightLiSample> {
-        todo!()
+        let render_from_light = self.base().render_from_light;
+        let p = render_from_light.apply_to_point(Point3f::new(0., 0., 0.));
+        let wi = (p - ctx.p()).normalize();
+        let wl = render_from_light.apply_inverse_vector(-wi);
+        let li = self.i(wl, lambda) / p.distance_squared(ctx.p());
+        let base = InteractionBase::new_boundary(p, 0., self.base.medium_interface);
+        let intr = SimpleInteraction::new(base);
+
+        Some(LightLiSample::new(li, wi, 1., Interaction::Simple(intr)))
     }
 
     fn pdf_li(
@@ -76,7 +87,7 @@ impl LightTrait for GoniometricLight {
         ))
     }
 
-    #[cfg(not(target_os = "cuda"))]
+    #[cfg(not(gpu))]
     fn phi(&self, lambda: SampledWavelengths) -> SampledSpectrum {
         let resolution = self.image.resolution();
         let mut sum_y = 0.;
diff --git a/shared/src/lights/infinite.rs b/shared/src/lights/infinite.rs
index db83094..1950f94 100644
--- a/shared/src/lights/infinite.rs
+++ b/shared/src/lights/infinite.rs
@@ -109,7 +109,7 @@ impl LightTrait for UniformInfiniteLight {
         None
     }
 
-    #[cfg(not(target_os = "cuda"))]
+    #[cfg(not(gpu))]
     fn phi(&self, lambda: SampledWavelengths) -> SampledSpectrum {
         4. * PI * PI * square(self.scene_radius) * self.scale * self.lemit.sample(&lambda)
     }
@@ -227,21 +227,17 @@ impl LightTrait for ImageInfiniteLight {
         self.image_le(uv, lambda)
     }
 
-    #[cfg(not(target_os = "cuda"))]
+    #[cfg(not(gpu))]
     fn phi(&self, lambda: SampledWavelengths) -> SampledSpectrum {
         let mut sum_l = SampledSpectrum::new(0.);
         let width = self.image.resolution().x();
         let height = self.image.resolution().y();
         for v in 0..height {
             for u in 0..width {
-                let mut rgb = RGB::default();
-                for c in 0..3 {
-                    rgb[c] = self.image.get_channel_with_wrap(
-                        Point2i::new(u, v),
-                        c,
-                        WrapMode::OctahedralSphere.into(),
-                    );
-                }
+                let rgb = RGB::from(self.image.get_channels_with_wrap::<3>(
+                    Point2i::new(u, v),
+                    WrapMode::OctahedralSphere.into(),
+                ));
                 sum_l += RGBIlluminantSpectrum::new(&self.image_color_space, rgb.clamp_zero())
                     .sample(&lambda);
             }
@@ -341,7 +337,7 @@ impl PortalInfiniteLight {
         (self.portal[1] - self.portal[0]).norm() * (self.portal[3] - self.portal[0]).norm()
     }
 
-    pub fn render_from_image(portal_frame: Frame, uv: Point2f) -> (Vector3f, Float) {
+    pub fn render_from_image_with(portal_frame: Frame, uv: Point2f) -> (Vector3f, Float) {
         let alpha = -PI / 2.0 + uv.x() * PI;
         let beta = -PI / 2.0 + uv.y() * PI;
 
@@ -354,6 +350,11 @@ impl PortalInfiniteLight {
 
         (portal_frame.from_local(w), duv_dw)
     }
+
+    #[inline]
+    pub fn render_from_image(&self, uv: Point2f) -> (Vector3f, Float) {
+        Self::render_from_image_with(self.portal_frame, uv)
+    }
 }
 
 impl LightTrait for PortalInfiniteLight {
@@ -370,7 +371,7 @@ impl LightTrait for PortalInfiniteLight {
     ) -> Option<LightLiSample> {
         let b = self.image_bounds(ctx.p())?;
         let (uv, map_pdf) = self.distribution.sample(u, b)?;
-        let (wi, duv_dw) = Self::render_from_image(self.portal_frame, uv);
+        let (wi, duv_dw) = self.render_from_image(uv);
         if duv_dw == 0. {
             return None;
         }
@@ -403,17 +404,34 @@ impl LightTrait for PortalInfiniteLight {
         }
     }
 
-    #[cfg(not(target_os = "cuda"))]
-    fn phi(&self, _lambda: SampledWavelengths) -> SampledSpectrum {
-        todo!()
+    #[cfg(not(gpu))]
+    fn phi(&self, lambda: SampledWavelengths) -> SampledSpectrum {
+        let mut sum_l = SampledSpectrum::new(0.);
+        let width = self.image.resolution().x();
+        let height = self.image.resolution().y();
+        for y in 0..height {
+            for x in 0..width {
+                let rgb = RGB::from(self.image.get_channels::<3>(Point2i::new(x, y)));
+                let st = Point2f::new(
+                    (x as Float + 0.5) / width as Float,
+                    (y as Float + 0.5) / height as Float,
+                );
+                let (_, duv_dw) = self.render_from_image(st);
+                sum_l += RGBIlluminantSpectrum::new(&self.image_color_space, rgb.clamp_zero())
+                    .sample(&lambda)
+                    / duv_dw;
+            }
+        }
+
+        self.scale * self.area() * sum_l / (width * height) as Float
     }
 
-    #[cfg(not(target_os = "cuda"))]
+    #[cfg(not(gpu))]
     fn preprocess(&mut self, scene_bounds: &Bounds3f) {
         (self.scene_center, self.scene_radius) = scene_bounds.bounding_sphere();
     }
 
-    #[cfg(not(target_os = "cuda"))]
+    #[cfg(not(gpu))]
     fn bounds(&self) -> Option<LightBounds> {
         None
     }
diff --git a/shared/src/lights/point.rs b/shared/src/lights/point.rs
index b35eda4..027ffef 100644
--- a/shared/src/lights/point.rs
+++ b/shared/src/lights/point.rs
@@ -51,14 +51,14 @@ impl LightTrait for PointLight {
         0.
     }
 
-    #[cfg(not(target_os = "cuda"))]
+    #[cfg(not(gpu))]
     fn phi(&self, lambda: SampledWavelengths) -> SampledSpectrum {
         4. * PI * self.scale * self.i.sample(&lambda)
     }
 
     fn preprocess(&mut self, _scene_bounds: &Bounds3f) {}
 
-    #[cfg(not(target_os = "cuda"))]
+    #[cfg(not(gpu))]
     fn bounds(&self) -> Option<LightBounds> {
         let p = self
             .base
diff --git a/shared/src/lights/projection.rs b/shared/src/lights/projection.rs
index 36ab79f..bc68c11 100644
--- a/shared/src/lights/projection.rs
+++ b/shared/src/lights/projection.rs
@@ -4,6 +4,7 @@ use crate::core::geometry::{
     Bounds2f, Bounds3f, Normal3f, Point2f, Point2i, Point3f, Ray, Vector3f, VectorLike, cos_theta,
 };
 use crate::core::image::Image;
+use crate::core::interaction::{Interaction, InteractionBase, SimpleInteraction};
 use crate::core::light::{
     LightBase, LightBounds, LightLiSample, LightSampleContext, LightTrait, LightType,
 };
@@ -33,7 +34,7 @@ pub struct ProjectionLight {
 }
 
 impl ProjectionLight {
-    pub fn i(&self, w: Vector3f, lambda: SampledWavelengths) -> SampledSpectrum {
+    pub fn i(&self, w: Vector3f, lambda: &SampledWavelengths) -> SampledSpectrum {
         if w.z() < self.hither {
             return SampledSpectrum::new(0.);
         }
@@ -44,10 +45,10 @@ impl ProjectionLight {
         let uv = Point2f::from(self.screen_bounds.offset(&Point2f::new(ps.x(), ps.y())));
         let mut rgb = RGB::default();
         for c in 0..3 {
-            rgb[c] = self.image.lookup_nearest_channel(uv, c as i32);
+            rgb[c] = self.image.lookup_nearest_channel(uv, c);
         }
-        let s = RGBIlluminantSpectrum::new(&*self.image_color_space, rgb.clamp_zero());
-        self.scale * s.sample(&lambda)
+        let s = RGBIlluminantSpectrum::new(&self.image_color_space, rgb.clamp_zero());
+        self.scale * s.sample(lambda)
     }
 }
 
@@ -58,12 +59,23 @@ impl LightTrait for ProjectionLight {
 
     fn sample_li(
         &self,
-        _ctx: &LightSampleContext,
+        ctx: &LightSampleContext,
         _u: Point2f,
-        _lambda: &SampledWavelengths,
+        lambda: &SampledWavelengths,
         _allow_incomplete_pdf: bool,
     ) -> Option<LightLiSample> {
-        todo!()
+        let render_from_light = self.base().render_from_light;
+        let p = render_from_light.apply_to_point(Point3f::new(0., 0., 0.));
+        let wi = (p - ctx.p()).normalize();
+        let wl = render_from_light.apply_inverse_vector(-wi);
+        let li = self.i(wl, lambda) / p.distance_squared(ctx.p());
+        if li.is_black() {
+            return None;
+        }
+        let base = InteractionBase::new_boundary(p, 0., self.base.medium_interface);
+        let intr = SimpleInteraction::new(base);
+
+        Some(LightLiSample::new(li, wi, 1., Interaction::Simple(intr)))
     }
 
     fn pdf_li(
@@ -72,7 +84,7 @@ impl LightTrait for ProjectionLight {
         _wi: Vector3f,
         _allow_incomplete_pdf: bool,
     ) -> Float {
-        todo!()
+        0.
     }
 
     fn phi(&self, lambda: SampledWavelengths) -> SampledSpectrum {
@@ -93,10 +105,10 @@ impl LightTrait for ProjectionLight {
                 let dwda = cos_theta(w).powi(3);
                 let mut rgb = RGB::default();
                 for c in 0..3 {
-                    rgb[c] = self.image.get_channel(Point2i::new(x, y), c as i32);
+                    rgb[c] = self.image.get_channel(Point2i::new(x, y), c);
                 }
 
-                let s = RGBIlluminantSpectrum::new(&*self.image_color_space, rgb.clamp_zero());
+                let s = RGBIlluminantSpectrum::new(&self.image_color_space, rgb.clamp_zero());
                 sum += s.sample(&lambda) * dwda;
             }
         }
diff --git a/shared/src/lights/spot.rs b/shared/src/lights/spot.rs
index 62d48df..5cad17c 100644
--- a/shared/src/lights/spot.rs
+++ b/shared/src/lights/spot.rs
@@ -65,7 +65,7 @@ impl LightTrait for SpotLight {
         0.
     }
 
-    #[cfg(not(target_os = "cuda"))]
+    #[cfg(not(gpu))]
     fn phi(&self, lambda: SampledWavelengths) -> SampledSpectrum {
         self.scale
             * self.iemit.sample(&lambda)
diff --git a/shared/src/materials/complex.rs b/shared/src/materials/complex.rs
index facb411..4a55468 100644
--- a/shared/src/materials/complex.rs
+++ b/shared/src/materials/complex.rs
@@ -30,7 +30,7 @@ pub struct HairMaterial {
 }
 
 impl HairMaterial {
-    #[cfg(not(target_os = "cuda"))]
+    #[cfg(not(gpu))]
     #[allow(clippy::too_many_arguments)]
     pub fn new(
         sigma_a: Ptr<SpectrumTexture>,
diff --git a/shared/src/shapes/bilinear.rs b/shared/src/shapes/bilinear.rs
index 30dadb4..4d3a413 100644
--- a/shared/src/shapes/bilinear.rs
+++ b/shared/src/shapes/bilinear.rs
@@ -98,7 +98,7 @@ impl BilinearPatchShape {
         Some([mesh.n[v0], mesh.n[v1], mesh.n[v2], mesh.n[v3]])
     }
 
-    #[cfg(not(target_os = "cuda"))]
+    #[cfg(not(gpu))]
     pub fn new(mesh: Ptr<BilinearPatchMesh>, blp_index: i32) -> Self {
         let mut bp = BilinearPatchShape {
             mesh,
diff --git a/src/lights/infinite.rs b/src/lights/infinite.rs
index ea4a08a..f387409 100644
--- a/src/lights/infinite.rs
+++ b/src/lights/infinite.rs
@@ -184,7 +184,7 @@ fn create_portal_light(
 
     // Build distribution
     let duv_dw = |p: Point2f| -> Float {
-        let (_, jacobian) = PortalInfiniteLight::render_from_image(portal_frame, p);
+        let (_, jacobian) = PortalInfiniteLight::render_from_image_with(portal_frame, p);
         jacobian
     };
     let d = remapped.get_sampling_distribution(
@@ -247,7 +247,7 @@ fn remap_image_through_portal(
                     (y as Float + 0.5) / height as Float,
                 );
 
-                let (w_world, _) = PortalInfiniteLight::render_from_image(*portal_frame, uv);
+                let (w_world, _) = PortalInfiniteLight::render_from_image_with(*portal_frame, uv);
                 let w_local = render_from_light.apply_inverse_vector(w_world).normalize();
                 let uv_equi = equal_area_sphere_to_square(w_local);