From b36fec7ba18d3015344d91859f02050395b04938 Mon Sep 17 00:00:00 2001
From: Tyrel Souza <tyrel@tyrelsouza.com>
Date: Thu, 25 Apr 2024 00:02:48 -0400
Subject: [PATCH] add triangles filled

---
 src/main.c     | 26 +++++++++--------
 src/triangle.c | 77 +++++++++++++++++++++++++++++++++++++++++++++++++-
 src/triangle.h |  4 +++
 3 files changed, 94 insertions(+), 13 deletions(-)

diff --git a/src/main.c b/src/main.c
index 3672d56..c804756 100644
--- a/src/main.c
+++ b/src/main.c
@@ -7,9 +7,7 @@
 #include "array.h"
 
 
-
-
-triangle_t* triangles_to_render = NULL;
+triangle_t *triangles_to_render = NULL;
 
 vec3_t camera_position = {0, 0, 0};
 float fov_factor = 640;
@@ -73,11 +71,12 @@ float check_backface_culling(const vec3_t *transformed_vertices) {// Check backf
     // Get vector subtraction of B-A and C-A
     vec3_t vector_ab = vec3_sub(vector_b, vector_a);
     vec3_t vector_ac = vec3_sub(vector_c, vector_a);
+    vec3_normalize(&vector_ab);
+    vec3_normalize(&vector_ac);
 
     // Get cross product to get the Normal N (to find perpendicular)
     // This is because left-handed coordinate system
     vec3_t normal = vec3_cross(vector_ab, vector_ac); // CLOCKWISE so A-B then A-C
-
     // normalize the Face Normal
     vec3_normalize(&normal);
 
@@ -145,24 +144,27 @@ void update(void) {
 }
 
 
-void render(void) {
-//    draw_grid();
 
-    //triangle array size
+void render(void) {
+    draw_grid();
+
+//    triangle array size
     int num_triangles = array_length(triangles_to_render);
     for (int i = 0; i < num_triangles; i++) {
         triangle_t triangle = triangles_to_render[i];
         uint32_t color = 0xFFFFFF00;
-        for (int j = 0; j < 3; j++) {
-            draw_rect(triangle.points[j].x, triangle.points[j].y, 3, 3, color);
-        }
-        draw_triangle(triangle.points[0].x, triangle.points[0].y,
+        draw_filled_triangle(triangle.points[0].x, triangle.points[0].y,
                       triangle.points[1].x, triangle.points[1].y,
                       triangle.points[2].x, triangle.points[2].y,
                       color);
-
+        draw_triangle(triangle.points[0].x, triangle.points[0].y,
+              triangle.points[1].x, triangle.points[1].y,
+              triangle.points[2].x, triangle.points[2].y,
+              0xFF000000);
     }
 
+
+
     render_color_buffer();
     clear_color_buffer(0xFF000000);
 
diff --git a/src/triangle.c b/src/triangle.c
index 07025ac..9171530 100644
--- a/src/triangle.c
+++ b/src/triangle.c
@@ -1,3 +1,78 @@
 #include "triangle.h"
+#include "display.h"
 
-// TODO
\ No newline at end of file
+
+void int_swap(int *a, int *b) {
+    int tmp = *a;
+    *a = *b;
+    *b = tmp;
+}
+
+void fill_flat_bottom_triangle(int x0, int y0, int x1, int y1, int x2, int y2, uint32_t color) {
+    // Start from top (x0, y0)
+    // calculate slope 1 and slope 2
+    // Y is independent as we loop over Y, we want the delta X change.
+    float inv_slope_1 = (float) (x1 - x0) / (float) (y1 - y0);
+    float inv_slope_2 = (float) (x2 - x0) / (float) (y2 - y0);
+
+    // start x_start and x_end from top vertex (x0,y0);
+    float x_start = x0;
+    float x_end = x0;
+    // loop all scan lines from y0 to y2
+    for (int y = y0; y <= y2; y++) {
+        draw_line(
+                x_start, y,
+                x_end, y,
+                color);
+        x_start += inv_slope_1;
+        x_end += inv_slope_2;
+    }
+}
+
+void fill_flat_top_triangle(int x0, int y0, int x1, int y1, int x2, int y2, uint32_t color) {
+    // start from bottom
+    // calculate slope 1 and slope 2
+    // Y is independent as we loop over Y, we want the delta X change.
+    float inv_slope_1 = (float) (x2 - x0) / (float) (y2 - y0);
+    float inv_slope_2 = (float) (x2 - x1) / (float) (y2 - y1);
+
+    // start x_start and x_end from top vertex (x0,y0);
+    float x_start = x2;
+    float x_end = x2;
+    // loop all scan lines from y0 to y2
+    for (int y = y2; y >= y0; y--) {
+        draw_line(
+                x_start, y,
+                x_end, y,
+                color);
+        x_start -= inv_slope_1;
+        x_end -= inv_slope_2;
+    }
+}
+
+void draw_filled_triangle(int x0, int y0, int x1, int y1, int x2, int y2, uint32_t color) {
+    //we need to sort the y coords  (y0 < y1 < y2)
+    if (y0 > y1) {
+        int_swap(&y0, &y1);
+        int_swap(&x0, &x1);
+    }
+    if (y1 > y2) {
+        int_swap(&y1, &y2);
+        int_swap(&x1, &x2);
+    }
+    if (y0 > y1) {
+        int_swap(&y0, &y1);
+        int_swap(&x0, &x1);
+    }
+
+    if (y1 == y2) {
+        fill_flat_bottom_triangle(x0, y0, x1, y1, x2, y2, color);
+    } else if (y0 == y2) {
+        fill_flat_top_triangle(x0, y0, x1, x1, x2, y2, color);
+    } else {
+        int My = y1;
+        int Mx = ((float) ((x2 - x0) * (y1 - y0)) / (float) (y2 - y0)) + (float) x0;
+        fill_flat_bottom_triangle(x0, y0, x1, y1, Mx, My, color);
+        fill_flat_top_triangle(x1, y1, Mx, My, x2, y2, color);
+    }
+}
\ No newline at end of file
diff --git a/src/triangle.h b/src/triangle.h
index 4592cba..94caa49 100644
--- a/src/triangle.h
+++ b/src/triangle.h
@@ -2,6 +2,7 @@
 #define RENDERER_TRIANGLE_H
 
 #include "vector.h"
+#include <stdint.h>
 
 typedef struct {
     int a;
@@ -13,4 +14,7 @@ typedef struct {
     vec2_t points[3];
 } triangle_t;
 
+void draw_filled_triangle(int x0, int y0, int x1, int y1, int x2, int y2, uint32_t color);
+
+
 #endif //RENDERER_TRIANGLE_H