Add model loading from OBJ and wireframe rendering

src/obj.c

@@ -0,0 +1,105 @@
+#include "obj.h"
+#include "aliases.h"
+#include "img.h"
+#include "mem_arena.h"
+#include "typed_list.h"
+#include "utils.h"
+#include <stdio.h>
+
+internal void render_wireframe_triangle(const Triangle *triangle,
+                                        const Model *model, Image *img,
+                                        Colour colour);
+internal void get_image_coordinates(const Vertex *vertex, const Image *img,
+                                    u64 *x, u64 *y);
+internal u64 ndc_to_image_coordinate(f32 value, u64 max);
+
+Model load_obj_file(Arena *arena, const char *filename) {
+  if (!arena) {
+    return NULL_MODEL;
+  }
+
+  FILE *fp = fopen(filename, "r");
+  if (!fp) {
+    return NULL_MODEL;
+  }
+
+  Model model = (Model){
+      .vertices = list_create(Vertex, arena),
+      .triangles = list_create(Triangle, arena),
+  };
+  if (!(model.vertices) || !(model.triangles)) {
+    return NULL_MODEL;
+  }
+
+  char line[8192];
+  char identifier[8];
+  Vertex vertex;
+  Triangle triangle;
+  f32 vx, vy, vz;
+  u64 fp0, fp1, fp2;
+  u64 ign_0_1, ign_0_2;
+  u64 ign_1_1, ign_1_2;
+  u64 ign_2_1, ign_2_2;
+  while (fgets(line, 8191, fp) != NULL) {
+    sscanf(line, "%s", identifier);
+    if (strncmp(identifier, "v", 8) == 0) {
+      sscanf(line + 2, "%f %f %f", &vx, &vy, &vz);
+      vertex.x = vx;
+      vertex.y = vy;
+      vertex.z = vz;
+      list_append(Vertex, arena, model.vertices, vertex);
+    } else if (strncmp(identifier, "f", 8) == 0) {
+      sscanf(line + 2, "%lu/%lu/%lu %lu/%lu/%lu %lu/%lu/%lu", &fp0, &ign_0_1,
+             &ign_0_2, &fp1, &ign_1_1, &ign_1_2, &fp2, &ign_2_1, &ign_2_2);
+      // OBJ indices start from 1
+      triangle.p0 = fp0 - 1;
+      triangle.p1 = fp1 - 1;
+      triangle.p2 = fp2 - 1;
+      list_append(Triangle, arena, model.triangles, triangle);
+    }
+  }
+
+  return model;
+}
+
+void render_wireframe_model(const Model *model, Image *img, Colour colour) {
+  Triangle triangle;
+
+  for (u64 i = 0; i < model->triangles->count; ++i) {
+    triangle = list_get(model->triangles, i);
+    render_wireframe_triangle(&triangle, model, img, colour);
+  }
+}
+
+internal void render_wireframe_triangle(const Triangle *triangle,
+                                        const Model *model, Image *img,
+                                        Colour colour) {
+  Vertex vertices[3] = {
+      list_get(model->vertices, triangle->p0),
+      list_get(model->vertices, triangle->p1),
+      list_get(model->vertices, triangle->p2),
+  };
+
+  Vertex v0, v1;
+  u64 x0, y0, x1, y1;
+  for (u64 i = 0; i < 3; ++i) {
+    v0 = vertices[i];
+    v1 = vertices[(i + 1) % 3];
+
+    get_image_coordinates(&v0, img, &x0, &y0);
+    get_image_coordinates(&v1, img, &x1, &y1);
+
+    draw_line(img, x0, y0, x1, y1, colour);
+  }
+}
+
+internal void get_image_coordinates(const Vertex *vertex, const Image *img,
+                                    u64 *x, u64 *y) {
+  *x = ndc_to_image_coordinate(vertex->x, img->width);
+  *y = ndc_to_image_coordinate(0.0f - vertex->y, img->height);
+}
+
+internal u64 ndc_to_image_coordinate(f32 value, u64 max) {
+  f32 result = (value + 1.0f) * max / 2.0f;
+  return clamp((u64)result, 0, max);
+}

src/obj.h

@@ -0,0 +1,38 @@
+#ifndef OBJ_H
+#define OBJ_H
+
+#include "aliases.h"
+#include "img.h"
+#include "mem_arena.h"
+#include "typed_list.h"
+
+#define NULL_MODEL ((Model){0})
+#define IS_NULL_MODEL(m) (m.vertices == NULL || m.triangles == NULL)
+
+typedef struct vertex Vertex;
+struct vertex {
+  f32 x;
+  f32 y;
+  f32 z;
+};
+
+typedef struct triangle Triangle;
+struct triangle {
+  u64 p0;
+  u64 p1;
+  u64 p2;
+};
+
+MAKE_LIST_TYPE(Vertex);
+MAKE_LIST_TYPE(Triangle);
+
+typedef struct model Model;
+struct model {
+  LIST_TYPE(Vertex) * vertices;
+  LIST_TYPE(Triangle) * triangles;
+};
+
+Model load_obj_file(Arena *arena, const char *filename);
+void render_wireframe_model(const Model *model, Image *img, Colour colour);
+
+#endif // OBJ_H