implement backface culling; basic lighting direction

src/main.cpp

@@ -12,6 +12,32 @@ const int windowHeight = 800;
 const int windowWidth = 800;
 Model *model = NULL;
 
+void line(Vec2i t0, Vec2i t1, TGAImage &image, TGAColor color) {
+    bool steep = false;
+
+    // if the line is steep, we transpose the image.
+    if (abs(t0.x - t1.x) < abs(t0.y - t1.y)) {
+        swap(t0.x, t0.y);
+        swap(t1.x, t1.y);
+        steep = true;
+    }
+    // Make it left to right.
+    if (t0.x > t1.x) {
+        swap(t0.x, t1.x);
+        swap(t0.y, t1.y);
+    }
+
+    for (int x = t0.x; x <= t1.x; x++) {
+        float t = (x - t0.x) / (float)(t1.x - t0.x);
+        int y = t0.y * (1.0 - t) + t1.y * t;
+        if (steep) {
+            image.set(y, x, color); // if transposed, de-transpose.
+        } else {
+            image.set(x, y, color);
+        }
+    }
+}
+
 Vec3f barycentric(Vec2i *pts, Vec2i P) {
     Vec3f u = Vec3f(pts[2].x - pts[0].x, pts[1].x - pts[0].x, pts[0].x - P.x) ^
               Vec3f(pts[2].y - pts[0].y, pts[1].y - pts[0].y, pts[0].y - P.y);
@@ -25,32 +51,7 @@ Vec3f barycentric(Vec2i *pts, Vec2i P) {
     return Vec3f(1.f - (u.x + u.y) / u.z, u.y / u.z, u.x / u.z);
 }
 
-void triangle(Vec2i t0, Vec2i t1, Vec2i t2, TGAImage &image, TGAColor color) {
+// Triangle function with binding box. 
-    if (t0.y == t1.y && t0.y == t2.y)
-        return;
-    if (t0.y > t1.y)
-        swap(t0, t1);
-    if (t0.y > t2.y)
-        swap(t0, t2);
-    if (t1.y > t2.y)
-        swap(t1, t2);
-    int total_height = t2.y - t0.y;
-    for (int i = 0; i < total_height; i++) {
-        bool second_half = i > t1.y - t0.y || t1.y == t0.y;
-        int segment_height = second_half ? t2.y - t1.y : t1.y - t0.y;
-        float alpha = (float)i / total_height;
-        float beta =
-            (float)(i - (second_half ? t1.y - t0.y : 0)) / segment_height;
-        Vec2i A = t0 + (t2 - t0) * alpha;
-        Vec2i B = second_half ? t1 + (t2 - t1) * beta : t0 + (t1 - t0) * beta;
-        if (A.x > B.x)
-            std::swap(A, B);
-        for (int j = A.x; j <= B.x; j++) {
-            image.set(j, t0.y + i, color);
-        }
-    }
-}
-
 void triangle(Vec2i *pts, TGAImage &image, TGAColor colour) {
     Vec2i boundingBoxMinimum(image.get_width() - 1, image.get_height() - 1);
     Vec2i boundingBoxMaximum(0, 0);
@@ -77,10 +78,37 @@ void triangle(Vec2i *pts, TGAImage &image, TGAColor colour) {
     }
 }
 
+// Triangle function via line sweeping.
+void triangle(Vec2i t0, Vec2i t1, Vec2i t2, TGAImage &image, TGAColor color) {
+    if (t0.y == t1.y && t0.y == t2.y)
+        return;
+    if (t0.y > t1.y)
+        swap(t0, t1);
+    if (t0.y > t2.y)
+        swap(t0, t2);
+    if (t1.y > t2.y)
+        swap(t1, t2);
+    int total_height = t2.y - t0.y;
+    for (int i = 0; i < total_height; i++) {
+        bool second_half = i > t1.y - t0.y || t1.y == t0.y;
+        int segment_height = second_half ? t2.y - t1.y : t1.y - t0.y;
+        float alpha = (float)i / total_height;
+        float beta =
+            (float)(i - (second_half ? t1.y - t0.y : 0)) / segment_height;
+        Vec2i A = t0 + (t2 - t0) * alpha;
+        Vec2i B = second_half ? t1 + (t2 - t1) * beta : t0 + (t1 - t0) * beta;
+        if (A.x > B.x)
+            std::swap(A, B);
+        for (int j = A.x; j <= B.x; j++) {
+            image.set(j, t0.y + i, color);
+        }
+    }
+}
+
+
+
 int main(int argc, char **argv) {
     TGAImage image(windowWidth, windowHeight, TGAImage::RGB);
-    Vec2i pts[3] = {Vec2i(30, 30), Vec2i(300, 90), Vec2i(570, 480)};
-    // triangle(pts, image, purple);
 
     // Model stuff.
     if (2 == argc)
@@ -88,18 +116,24 @@ int main(int argc, char **argv) {
     else
         model = new Model("../obj/wolf_head.obj");
 
+    
+    Vec3f lightDirection(0,0,-1);
+
     for (int i = 0; i < model->nfaces(); i++) {
         vector<int> face = model->face(i);
         Vec2i screenCoordinates[3];
+        Vec3f worldCoordinates[3];
         for (int j = 0; j < 3; j++) {
-            Vec3f worldCoordinates = model->vert(face[j]);
+            Vec3f v = model->vert(face[j]);
-            screenCoordinates[j] =
+            screenCoordinates[j] = Vec2i((v.x + 1.0) * windowWidth / 2.0, (v.y + 1.0) * windowHeight / 2.0);
-                Vec2i((worldCoordinates.x + 1) * windowWidth / 2.0,
+            worldCoordinates[j] = v;
-                      (worldCoordinates.y + 1.0) * windowHeight / 2.0);
         }
-        triangle(screenCoordinates[0], screenCoordinates[1],
+        Vec3f n = (worldCoordinates[2] - worldCoordinates[0]) ^ (worldCoordinates[1] - worldCoordinates[0]);
+        n.normalize();
+        float intensity = n * lightDirection;
+        if (intensity > 0) triangle(screenCoordinates[0], screenCoordinates[1],
                  screenCoordinates[2], image,
-                 TGAColor(rand() % 255, rand() % 255, rand() % 255, 255));
+                 TGAColor(intensity * 255, intensity * 255, intensity * 255, 255));
     }
     image.flip_vertically();
     image.write_tga_file("output.tga");