292 lines
8.4 KiB
C++
292 lines
8.4 KiB
C++
#define _USE_MATH_DEFINES
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/*
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* 基于三角形面片的步进式纹理变换康奈尔盒渲染器（无递归，无AO/反射，仅面片遮挡关系）
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* 编译: g++ cornell_box_tri_step_transform.cpp -std=c++11 -O2 -o cornell_box_tri
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* 运行: ./cornell_box_tri
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*/
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#include <algorithm>
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#include <cmath>
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#include <cstdio>
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#include <iostream>
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#include <vector>
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constexpr float EPS = 1e-6f;
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constexpr float INF = 1e30f;
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struct Vec3 {
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float x, y, z;
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Vec3(float xx = 0, float yy = 0, float zz = 0) : x(xx), y(yy), z(zz) {
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}
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Vec3 operator+(const Vec3 &b) const {
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return Vec3(x + b.x, y + b.y, z + b.z);
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}
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Vec3 operator-(const Vec3 &b) const {
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return Vec3(x - b.x, y - b.y, z - b.z);
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}
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Vec3 operator*(float s) const {
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return Vec3(x * s, y * s, z * s);
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}
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float dot(const Vec3 &b) const {
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return x * b.x + y * b.y + z * b.z;
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}
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Vec3 cross(const Vec3 &b) const {
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return Vec3(
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y * b.z - z * b.y,
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z * b.x - x * b.z,
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x * b.y - y * b.x);
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}
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float length() const {
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return std::sqrt(x * x + y * y + z * z);
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}
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Vec3 normalized() const {
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float l = length();
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return (*this) * (1.0f / l);
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}
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};
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struct Color {
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float r, g, b;
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Color(float rr = 0, float gg = 0, float bb = 0) : r(rr), g(gg), b(bb) {
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}
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Color operator*(float s) const {
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return Color(r * s, g * s, b * s);
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}
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Color operator+(const Color &c) const {
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return Color(r + c.r, g + c.g, b + c.b);
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}
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void clamp() {
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r = fmaxf(0.0f, fminf(1.0f, r));
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g = fmaxf(0.0f, fminf(1.0f, g));
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b = fmaxf(0.0f, fminf(1.0f, b));
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}
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};
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struct Texture {
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virtual Color at(float u, float v) const = 0;
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virtual ~Texture() {
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}
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};
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struct SolidTexture : Texture {
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Color c;
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SolidTexture(Color cc) : c(cc) {
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}
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Color at(float, float) const override {
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return c;
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}
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};
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struct CheckerTexture : Texture {
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Color a, b;
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float scale;
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CheckerTexture(Color c1, Color c2, float s = 10) : a(c1), b(c2), scale(s) {
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}
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Color at(float u, float v) const override {
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int xx = int(floor(u * scale)), yy = int(floor(v * scale));
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return ((xx + yy) % 2 == 0) ? a : b;
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}
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};
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struct MetalTexture : Texture {
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Color tint;
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MetalTexture(Color tt) : tint(tt) {
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}
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Color at(float, float) const override {
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return tint;
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}
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};
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struct Tri {
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Vec3 v0, v1, v2;
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Vec3 n; // 法线
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Vec3 uv0, uv1, uv2; // uv.xy
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Texture *tex;
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Tri(Vec3 a, Vec3 b, Vec3 c, Vec3 t0, Vec3 t1, Vec3 t2, Texture *tx)
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: v0(a), v1(b), v2(c), uv0(t0), uv1(t1), uv2(t2), tex(tx) {
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n = (v1 - v0).cross(v2 - v0).normalized();
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}
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// 射线相交
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bool intersect(const Vec3 &o, const Vec3 &d, float &t, float &u, float &v) const {
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// Moller-Trumbore
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Vec3 e1 = v1 - v0, e2 = v2 - v0, h = d.cross(e2), s = o - v0;
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float a = e1.dot(h);
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if (fabs(a) < EPS)
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return false;
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float f = 1.f / a;
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u = f * s.dot(h);
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if (u < 0 || u > 1)
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return false;
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Vec3 q = s.cross(e1);
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v = f * d.dot(q);
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if (v < 0 || u + v > 1)
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return false;
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t = f * e2.dot(q);
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return t > EPS;
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}
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// barycentric -> uv
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void bary2uv(float b0, float b1, float b2, float &u, float &v) const {
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u = uv0.x * b0 + uv1.x * b1 + uv2.x * b2;
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v = uv0.y * b0 + uv1.y * b1 + uv2.y * b2;
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}
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// 在射线上与面片交点对应的纹理坐标
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bool texcoord_at_hit(const Vec3 &o, const Vec3 &d, float &t, float &outu, float &outv) const {
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float uu, vv;
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if (!intersect(o, d, t, uu, vv))
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return false;
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float w = 1 - uu - vv;
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bary2uv(w, uu, vv, outu, outv);
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return true;
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}
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};
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struct Camera {
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Vec3 pos, target, up;
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float fov;
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Camera(Vec3 p, Vec3 t, Vec3 u, float f) : pos(p), target(t), up(u), fov(f) {
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}
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};
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// Cornell box三角分割，每个面（矩形）分两个三角
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struct Scene {
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std::vector<Tri> tris;
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std::vector<Texture *> textures; // 管理资源释放
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~Scene() {
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for (Texture *t : textures)
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delete t;
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}
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Scene() {
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// 盒体(-1~1)
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Texture *red = new SolidTexture(Color(0.8, 0.15, 0.15)),
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*green = new SolidTexture(Color(0.15, 0.8, 0.15)),
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*white = new SolidTexture(Color(0.8, 0.8, 0.8)),
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*checker = new CheckerTexture(Color(0.9, 0.9, 0.9), Color(0.1, 0.1, 0.1), 8);
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textures = { red, green, white, checker };
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// --- 左壁(红)
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pushQuad(-1, -1, -1, -1, 1, -1, -1, 1, 1, -1, -1, 1, red);
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// --- 右壁(绿)
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pushQuad(1, -1, 1, 1, 1, 1, 1, 1, -1, 1, -1, -1, green);
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// --- 地板(棋盘)
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pushQuad(-1, -1, 1, 1, -1, 1, 1, -1, -1, -1, -1, -1, checker);
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// --- 顶
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pushQuad(-1, 1, 1, -1, 1, -1, 1, 1, -1, 1, 1, 1, white);
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// --- 背面(白)
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pushQuad(-1, -1, -1, 1, -1, -1, 1, 1, -1, -1, 1, -1, white);
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// 添加一个立方体（中心(-0.4,-0.5,0.2)，尺寸0.4）
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pushBox(-0.4f, -0.7f, 0.2f, 0.20f, white);
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}
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// 面片顶点uv为(0,0),(1,0),(1,1),(0,1)
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void pushQuad(float x0, float y0, float z0, float x1, float y1, float z1,
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float x2, float y2, float z2, float x3, float y3, float z3, Texture *t) {
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tris.emplace_back(Vec3(x0, y0, z0), Vec3(x1, y1, z1), Vec3(x2, y2, z2),
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Vec3(0, 0, 0), Vec3(1, 0, 0), Vec3(1, 1, 0), t);
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tris.emplace_back(Vec3(x0, y0, z0), Vec3(x2, y2, z2), Vec3(x3, y3, z3),
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Vec3(0, 0, 0), Vec3(1, 1, 0), Vec3(0, 1, 0), t);
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}
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// 六面体
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void pushBox(float cx, float cy, float cz, float r, Texture *t) {
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float x = cx, y = cy, z = cz, s = r;
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float X[2] = { x - s, x + s }, Y[2] = { y - s, y + s }, Z[2] = { z - s, z + s };
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// 六面六个pushQuad
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pushQuad(X[0], Y[0], Z[0], X[1], Y[0], Z[0], X[1], Y[1], Z[0], X[0], Y[1], Z[0], t); // 后
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pushQuad(X[0], Y[0], Z[1], X[1], Y[0], Z[1], X[1], Y[1], Z[1], X[0], Y[1], Z[1], t); // 前
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pushQuad(X[0], Y[0], Z[0], X[0], Y[1], Z[0], X[0], Y[1], Z[1], X[0], Y[0], Z[1], t); // 左
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pushQuad(X[1], Y[0], Z[0], X[1], Y[1], Z[0], X[1], Y[1], Z[1], X[1], Y[0], Z[1], t); // 右
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pushQuad(X[0], Y[1], Z[0], X[1], Y[1], Z[0], X[1], Y[1], Z[1], X[0], Y[1], Z[1], t); // 上
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pushQuad(X[0], Y[0], Z[0], X[1], Y[0], Z[0], X[1], Y[0], Z[1], X[0], Y[0], Z[1], t); // 下
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}
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};
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struct Viewport {
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int w, h;
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std::vector<Color> pixels;
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Viewport(int W, int H) : w(W), h(H), pixels(W * H) {
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}
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void set(int x, int y, const Color &c) {
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if (x >= 0 && y >= 0 && x < w && y < h)
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pixels[y * w + x] = c;
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}
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const Color &get(int x, int y) const {
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return pixels[y * w + x];
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}
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};
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struct Cand {
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float t; // 距离
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Color c;
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Cand(float _t, const Color &_c) : t(_t), c(_c) {
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}
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};
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bool dist_cmp(const Cand &a, const Cand &b) {
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return a.t > b.t;
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}
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// 主渲染器
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void render(const Scene &scene, const Camera &cam, Viewport &vp) {
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// 视锥参数
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Vec3 forward = (cam.target - cam.pos).normalized();
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Vec3 right = forward.cross(cam.up).normalized();
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Vec3 up = right.cross(forward);
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float aspect = 1.0 * vp.w / vp.h;
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float imagePlaneDist = 1.0;
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float scale = tanf(cam.fov * 0.5f * M_PI / 180.f) * imagePlaneDist;
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for (int y = 0; y < vp.h; ++y)
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for (int x = 0; x < vp.w; ++x) {
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float fx = (2 * (x + 0.5f) / vp.w - 1) * aspect * scale;
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float fy = (1 - 2 * (y + 0.5f) / vp.h) * scale;
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Vec3 dir = (forward * imagePlaneDist + right * fx + up * fy).normalized();
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std::vector<Cand> cands;
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for (const auto &tri : scene.tris) {
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float t, u, v;
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if (tri.intersect(cam.pos, dir, t, u, v)) {
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float w = 1 - u - v, uu, vv;
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tri.bary2uv(w, u, v, uu, vv);
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Color col = tri.tex->at(uu, vv);
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cands.emplace_back(t, col);
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}
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}
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if (cands.empty()) {
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vp.set(x, y, Color(0, 0, 0));
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continue;
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}
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std::sort(cands.begin(), cands.end(), dist_cmp);
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Color col = cands.front().c;
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col.clamp();
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vp.set(x, y, col);
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}
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std::cerr << "Rendered." << std::endl;
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}
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void writePPM(const Viewport &vp, const char *fn) {
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FILE *f = fopen(fn, "wb");
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fprintf(f, "P6\n%d %d\n255\n", vp.w, vp.h);
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for (int y = 0; y < vp.h; ++y)
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for (int x = 0; x < vp.w; ++x) {
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Color c = vp.get(x, y);
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c.clamp();
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unsigned char rr = (unsigned char)(pow(c.r, 1 / 2.2f) * 255);
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unsigned char gg = (unsigned char)(pow(c.g, 1 / 2.2f) * 255);
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unsigned char bb = (unsigned char)(pow(c.b, 1 / 2.2f) * 255);
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fwrite(&rr, 1, 1, f);
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fwrite(&gg, 1, 1, f);
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fwrite(&bb, 1, 1, f);
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}
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fclose(f);
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}
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int main() {
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int width = 512, height = 512;
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Scene scene;
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Camera cam(
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Vec3(0, 0, 4),
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Vec3(0, 0, 0),
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Vec3(0, 1, 0),
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50.f);
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Viewport vp(width, height);
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render(scene, cam, vp);
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writePPM(vp, "out.ppm");
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std::cout << "Saved to out.ppm\n";
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return 0;
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}
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