CDE

Task/Death-Star/D/death-star.d

@@ -0,0 +1,109 @@
+import std.stdio, std.math, std.numeric, std.algorithm;
+
+struct V3 {
+    double[3] v;
+
+    @property V3 normalize() pure nothrow const {
+        immutable double len = dotProduct(v, v).sqrt();
+        //return V3(v[] / len);
+        return V3([v[0] / len, v[1] / len, v[2] / len]);
+    }
+
+    double dot(in ref V3 y) pure nothrow const {
+        immutable double d = dotProduct(v, y.v);
+        return d < 0 ? -d : 0;
+    }
+}
+
+
+const struct Sphere { double cx, cy, cz, r; }
+
+void drawSphere(in double k, in double ambient, in V3 light) nothrow {
+    /** Check if a ray (x,y, -inf).(x, y, inf) hits a sphere; if so,
+    return the intersecting z values.  z1 is closer to the eye */
+    static bool hitSphere(in ref Sphere sph,
+                          in double x0, in double y0,
+                          out double z1,
+                          out double z2) pure nothrow {
+        immutable double x = x0 - sph.cx;
+        immutable double y = y0 - sph.cy;
+        immutable double zsq = sph.r ^^ 2 - (x ^^ 2 + y ^^ 2);
+        if (zsq < 0)
+            return false;
+        immutable double szsq = sqrt(zsq);
+        z1 = sph.cz - szsq;
+        z2 = sph.cz + szsq;
+        return true;
+    }
+
+    enum string shades = ".:!*oe&#%@";
+    // positive and negative spheres
+    immutable pos = Sphere(20, 20, 0, 20);
+    immutable neg = Sphere(1, 1, -6, 20);
+
+    foreach (int i; cast(int)floor(pos.cy - pos.r) ..
+                    cast(int)ceil(pos.cy + pos.r) + 1) {
+        immutable double y = i + 0.5;
+        jloop:
+        foreach (int j; cast(int)floor(pos.cx - 2 * pos.r) ..
+                        cast(int)ceil(pos.cx + 2 * pos.r) + 1) {
+            immutable double x = (j - pos.cx) / 2.0 + 0.5 + pos.cx;
+
+            enum Hit { background, posSphere, negSphere }
+            Hit hitResult;
+            double zb1, zs2;
+            {
+                double zb2, zs1;
+                if (!hitSphere(pos, x, y, zb1, zb2)) {
+                    // Ray lands in blank space, draw bg
+                    hitResult = Hit.background;
+                } else if (!hitSphere(neg, x, y, zs1, zs2)) {
+                    // Ray hits pos sphere but not neg one,
+                    // draw pos sphere surface
+                    hitResult = Hit.posSphere;
+                } else if (zs1 > zb1) {
+                    // ray hits both, but pos front surface is closer
+                    hitResult = Hit.posSphere;
+                } else if (zs2 > zb2) {
+                    // pos sphere surface is inside neg sphere,
+                    // show bg
+                    hitResult = Hit.background;
+                } else if (zs2 > zb1) {
+                    // Back surface on neg sphere is inside pos
+                    // sphere, the only place where neg sphere
+                    // surface will be shown
+                    hitResult = Hit.negSphere;
+                } else {
+                    hitResult = Hit.posSphere;
+                }
+            }
+
+            V3 vec_;
+            final switch (hitResult) {
+                case Hit.background:
+                    putchar(' ');
+                    continue jloop;
+                case Hit.posSphere:
+                    vec_ = V3([x - pos.cx, y - pos.cy, zb1 - pos.cz]);
+                    break;
+                case Hit.negSphere:
+                    vec_ = V3([neg.cx - x, neg.cy - y, neg.cz - zs2]);
+                    break;
+            }
+            immutable V3 nvec = vec_.normalize;
+
+            immutable double b = light.dot(nvec) ^^ k + ambient;
+            int intensity = cast(int)((1 - b) * shades.length);
+            intensity = min(shades.length, max(0, intensity));
+            putchar(shades[intensity]);
+        }
+
+        putchar('\n');
+    }
+}
+
+
+void main() {
+    enum light = V3([-50, 30, 50]).normalize;
+    drawSphere(2, 0.5, light);
+}