Point cloud rendering

Author: ssloy

CMakeLists.txt

@@ -21,7 +21,7 @@ endif()
 
 find_package(OpenMP COMPONENTS CXX)
 
-set(SOURCES main.cpp tgaimage.cpp)
+set(SOURCES main.cpp model.cpp tgaimage.cpp)
 
 add_executable(${PROJECT_NAME} ${SOURCES})
 target_link_libraries(${PROJECT_NAME} PRIVATE $<$<BOOL:${OpenMP_CXX_FOUND}>:OpenMP::OpenMP_CXX>)

geometry.h

@@ -0,0 +1,24 @@
+#pragma once
+#include <cmath>
+#include <cassert>
+#include <iostream>
+
+template<int n> struct vec {
+ double data[n] = {0};
+ double& operator[](const int i) { assert(i>=0 && i<n); return data[i]; }
+ double operator[](const int i) const { assert(i>=0 && i<n); return data[i]; }
+};
+
+template<int n> std::ostream& operator<<(std::ostream& out, const vec<n>& v) {
+ for (int i=0; i<n; i++) out << v[i] << " ";
+ return out;
+}
+
+template<> struct vec<3> {
+ double x = 0, y = 0, z = 0;
+ double& operator[](const int i) { assert(i>=0 && i<3); return i ? (1==i ? y : z) : x; }
+ double operator[](const int i) const { assert(i>=0 && i<3); return i ? (1==i ? y : z) : x; }
+};
+
+typedef vec<3> vec3;
+

main.cpp

@@ -1,6 +1,12 @@
 #include <cmath>
+#include <tuple>
+#include "geometry.h"
+#include "model.h"
 #include "tgaimage.h"
 
+constexpr int width = 800;
+constexpr int height = 800;
+
 constexpr TGAColor white = {255, 255, 255, 255}; // attention, BGRA order
 constexpr TGAColor green = { 0, 255, 0, 255};
 constexpr TGAColor red = { 0, 0, 255, 255};
@@ -32,23 +38,25 @@ void line(int ax, int ay, int bx, int by, TGAImage &framebuffer, TGAColor color)
  }
 }
 
-int main(int argc, char** argv) {
- constexpr int width = 64;
- constexpr int height = 64;
- TGAImage framebuffer(width, height, TGAImage::RGB);
+std::tuple<int,int> project(vec3 v) { // First of all, (x,y) is an orthogonal projection of the vector (x,y,z).
+ return { (v.x + 1.) * width/2, // Second, since the input models are scaled to have fit in the [-1,1]^3 world coordinates,
+  (v.y + 1.) * height/2 }; // we want to shift the vector (x,y) and then scale it to span the entire screen.
+}
 
- int ax = 7, ay = 3;
- int bx = 12, by = 37;
- int cx = 62, cy = 53;
+int main(int argc, char** argv) {
+ if (argc != 2) {
+ std::cerr << "Usage: " << argv[0] << " obj/model.obj" << std::endl;
+ return 1;
+ }
 
- line(ax, ay, bx, by, framebuffer, blue);
- line(cx, cy, bx, by, framebuffer, green);
- line(cx, cy, ax, ay, framebuffer, yellow);
- line(ax, ay, cx, cy, framebuffer, red);
+ Model model(argv[1]);
+ TGAImage framebuffer(width, height, TGAImage::RGB);
 
- framebuffer.set(ax, ay, white);
- framebuffer.set(bx, by, white);
- framebuffer.set(cx, cy, white);
+ for (int i=0; i<model.nverts(); i++) { // iterate through all vertices
+ vec3 v = model.vert(i); // get i-th vertex
+ auto [x, y] = project(v); // project it to the screen
+ framebuffer.set(x, y, white);
+ }
 
  framebuffer.write_tga_file("framebuffer.tga");
  return 0;

model.cpp

@@ -0,0 +1,45 @@
+#include <fstream>
+#include <sstream>
+#include "model.h"
+
+Model::Model(const std::string filename) {
+ std::ifstream in;
+ in.open(filename, std::ifstream::in);
+ if (in.fail()) return;
+ std::string line;
+ while (!in.eof()) {
+ std::getline(in, line);
+ std::istringstream iss(line.c_str());
+ char trash;
+ if (!line.compare(0, 2, "v ")) {
+ iss >> trash;
+ vec3 v;
+ for (int i : {0,1,2}) iss >> v[i];
+ verts.push_back(v);
+ } else if (!line.compare(0, 2, "f ")) {
+ int f,t,n, cnt = 0;
+ iss >> trash;
+ while (iss >> f >> trash >> t >> trash >> n) {
+ facet_vrt.push_back(--f);
+ cnt++;
+ }
+ if (3!=cnt) {
+ std::cerr << "Error: the obj file is supposed to be triangulated" << std::endl;
+ return;
+ }
+ }
+ }
+ std::cerr << "# v# " << nverts() << " f# " << nfaces() << std::endl;
+}
+
+int Model::nverts() const { return verts.size(); }
+int Model::nfaces() const { return facet_vrt.size()/3; }
+
+vec3 Model::vert(const int i) const {
+ return verts[i];
+}
+
+vec3 Model::vert(const int iface, const int nthvert) const {
+ return verts[facet_vrt[iface*3+nthvert]];
+}
+

model.h

@@ -0,0 +1,14 @@
+#include <vector>
+#include "geometry.h"
+
+class Model {
+ std::vector<vec3> verts = {}; // array of vertices
+ std::vector<int> facet_vrt = {}; // per-triangle index in the above array
+public:
+ Model(const std::string filename);
+ int nverts() const; // number of vertices
+ int nfaces() const; // number of triangles
+ vec3 vert(const int i) const; // 0 <= i < nverts()
+ vec3 vert(const int iface, const int nthvert) const; // 0 <= iface <= nfaces(), 0 <= nthvert < 3
+};
+