1 files changed, 160 insertions, 0 deletions
diff --git a/src/main.c b/src/main.c
new file mode 100644
index 0000000..6e37e37
--- /dev/null
+++ b/src/main.c
@@ -0,0 +1,160 @@
+#include <limits.h>
+#include <float.h>
+#include <stdint.h>
+#include <math.h>
+
+#include "vecmath.h"
+#include "picture.h"
+
+typedef enum {
+    kAmbientLight,
+    kPointLight,
+    kDirectionalLight,
+} LightType;
+
+typedef struct {
+    LightType type;
+    float intensity;
+    Vec3f vec;
+} Light;
+
+Vec3f screen_proj(int width, int height, Vec2i sp) {
+    Vec3f ret;
+    float maxlen = width > height ? width : height; 
+    ret.z = 1.0;
+    ret.x = (sp.x - width / 2.0) / maxlen;
+    ret.y = (-sp.y + height / 2.0) / maxlen;
+    return ret;
+}
+
+typedef struct {
+    Vec3f center;
+    float r;
+    Color color;
+} Ball;
+
+Ball balls[] = {
+    {
+        .center = {.x = 0, .y = -1, .z = 3},
+        .r = 1,
+    },
+    {
+        .center = {.x = 2, .y = 0, .z = 4},
+        .r = 1,
+    },
+    {
+        .center = {.x = -2, .y = 0, .z = 4},
+        .r = 1,
+    },
+    {
+        .center = {0, -5001, 0},
+        .r = 5000,
+    },
+};
+
+Light lights[] = {
+    {
+        .type = kAmbientLight,
+        .intensity = 0.2,
+    },
+    {
+        .type = kPointLight,
+        .intensity = 0.6,
+        .vec = {2.0, 1.0, 0.0},
+    },
+    {
+        .type = kDirectionalLight,
+        .intensity = 0.2,
+        .vec = {1.0, 4.0, 4.0}
+    },
+};
+
+
+Color gBackgroupColor = {0,0,0};
+
+void init_color() {
+    balls[0].color = icolor(0x95e1d3);
+    balls[1].color = icolor(0xfce38a);
+    balls[2].color = icolor(0xf38181);
+    balls[3].color = icolor(0xeaffd0);
+    gBackgroupColor = icolor(0xeaeaea);
+}
+
+float ball_intersect(Vec3f start, Vec3f ray, Ball *ball) {
+    Vec3f sc = vec3f_sub(start, ball->center);
+    float a = vec3f_dot(ray, ray);
+    float b = 2 * vec3f_dot(sc, ray);
+    float c = vec3f_dot(sc, sc) - ball->r * ball->r;
+    float delta = b*b - 4*a*c;
+    if (delta < 0) {
+        return -1;
+    }
+    float t1 = (-b + sqrt(delta)) / (2*a);
+    float t2 = (-b - sqrt(delta)) / (2*a);
+    return t1 < t2 ? t1 : t2;
+}
+
+
+Color ball_surface_color(Ball *ball, Vec3f point) {
+    Vec3f norm = vec3f_normalize(vec3f_sub(point, ball->center));
+    float amp = 0;
+    for (int i = 0; i < sizeof(lights) / sizeof(Light); i++) {
+        if (lights[i].type == kAmbientLight) {
+            amp += lights[i].intensity;
+        } else if (lights[i].type == kPointLight) {
+            Vec3f l = vec3f_normalize(vec3f_sub(lights[i].vec, point));
+            float prod = vec3f_dot(l, norm);
+            if (prod > 0) amp += prod * lights[i].intensity;
+        } else if (lights[i].type == kDirectionalLight) {
+            Vec3f l = vec3f_normalize(lights[i].vec);
+            float prod = vec3f_dot(l, norm);
+            if (prod > 0) amp += prod * lights[i].intensity;
+        }
+    }
+    return (Color){
+        ball->color.r * amp,
+        ball->color.g * amp,
+        ball->color.b * amp
+    };
+}
+
+Color calc_color(Vec3f v) {
+    Vec3f start = {.x = 0, .y = 0, .z = 0};
+    float tmin = 0.1;
+    float tmax = FLT_MAX;
+
+    int nearest_idx = -1;
+    float t_nearest = FLT_MAX;
+    for (int i = 0; i < sizeof(balls) / sizeof(Ball); i++) {
+        float t = ball_intersect(start, v, &balls[i]);
+        if (t < t_nearest && t < tmax && t > tmin) {
+            t_nearest = t;
+            nearest_idx = i;
+        }
+    }
+    if (nearest_idx >= 0) {
+        Vec3f intersection = vec3f_add(start, vec3f_mul(t_nearest, v));
+        return ball_surface_color(&balls[nearest_idx], intersection);
+    } else {
+        return gBackgroupColor;
+    }
+}
+
+
+int main() {
+    init_color();
+    int img_w = 1280;
+    int img_h = 720;
+    Picture pic = new_picture(img_w, img_h);
+    for (int x = 0; x < img_w; x++) {
+        for (int y = 0; y < img_h; y++) {
+            Vec2i screen_pos = {x, y};
+            Vec3f v = screen_proj(img_w, img_h, screen_pos);
+            set_pixel(pic, screen_pos, calc_color(v));
+        }
+    }
+    writeBMP("test.bmp", pic);
+    delete_picture(pic);
+    return 0;
+}
+