feat(examples): add the C++ benchmark and three test targets

A C++ consumer of the C archives, plus maths, scene and image tests driven by
meowc test.

examples/raytracer/tests/scene_test.c

@@ -0,0 +1,50 @@
+#include "rt_scene.h"
+#include "studio_scene.h"
+#include <math.h>
+#include <stdio.h>
+
+static int failures = 0;
+
+static void check(const char *what, int cond) {
+    if (!cond) {
+        fprintf(stderr, "  %s: failed\n", what);
+        failures++;
+    }
+}
+
+int main(void) {
+    check("the generated scene has spheres", studio_sphere_count > 0);
+
+    /* One unit sphere at the origin, hit straight down the -z axis. */
+    static const sphere one[] = {{{0, 0, 0}, 1.0, {MAT_LAMBERT, {0.5, 0.5, 0.5}, 0.0}}};
+    scene sc = {one, 1, {0, 0, 0}};
+
+    ray r = {{0, 0, 5}, {0, 0, -1}};
+    hit h;
+    check("a ray aimed at the sphere hits it", scene_hit(&sc, r, 1e-4, 1e30, &h));
+    check("it hits the near face", fabs(h.t - 4.0) < 1e-9);
+    check("the normal faces the ray", fabs(h.normal.z - 1.0) < 1e-9);
+    check("the hit is on the outside", h.front == 1);
+
+    ray miss = {{0, 5, 5}, {0, 0, -1}};
+    check("a ray that passes above misses", !scene_hit(&sc, miss, 1e-4, 1e30, &h));
+
+    /* Starting inside, the first crossing is the far wall. */
+    ray inside = {{0, 0, 0}, {0, 0, -1}};
+    check("a ray from the centre still hits", scene_hit(&sc, inside, 1e-4, 1e30, &h));
+    check("and reports the inside face", h.front == 0);
+
+    /* The interval bounds are respected. */
+    check("a hit beyond tmax is rejected", !scene_hit(&sc, r, 1e-4, 1.0, &h));
+
+    /* Nearest sphere wins when two overlap the ray. */
+    static const sphere two[] = {
+        {{0, 0, 0}, 1.0, {MAT_LAMBERT, {1, 0, 0}, 0.0}},
+        {{0, 0, 2.5}, 0.5, {MAT_METAL, {0, 1, 0}, 0.0}},
+    };
+    scene both = {two, 2, {0, 0, 0}};
+    check("the closer sphere is chosen", scene_hit(&both, r, 1e-4, 1e30, &h) && h.mat.kind == MAT_METAL);
+
+    if (failures == 0) printf("  scene: every assertion held\n");
+    return failures == 0 ? 0 : 1;
+}