From 0701b9b3032ee1197cac8eface3639a5d6a646fd Mon Sep 17 00:00:00 2001
From: natsirt867 <natsirt867@gmail.com>
Date: Thu, 1 Jan 2026 16:29:17 -0600
Subject: [PATCH] added texture mapping functionality

---
 src/main.c     |  2 +-
 src/texture.c  |  2 +-
 src/triangle.c | 86 +++++++++++++++++++++++++++++++++++++++++++++++---
 src/triangle.h |  6 +++-
 4 files changed, 89 insertions(+), 7 deletions(-)

diff --git a/src/main.c b/src/main.c
index b7514d5..cea89c7 100644
--- a/src/main.c
+++ b/src/main.c
@@ -223,7 +223,7 @@ void update(void){
             projected_points[j].y *= (window_height / 2.0);
 
             // Invert the y values to account for flipped screen y coordinates
-            projected_points[j].y *= -1;
+            //projected_points[j].y *= -1;
 
             // translate the projected points to the middle of the screen
             projected_points[j].x += (window_width / 2.0);
diff --git a/src/texture.c b/src/texture.c
index 60555c5..4aa8f8a 100755
--- a/src/texture.c
+++ b/src/texture.c
@@ -70,4 +70,4 @@ const uint8_t REDBRICK_TEXTURE[] = {
     0x2c, 0x2c, 0x2c, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x48, 0x48, 0x48, 0xff, 0x54, 0x54, 0x54, 0xff, 0x48, 0x48, 0x48, 0xff, 0x38, 0x38, 0x38, 0xff, 0x34, 0x34, 0x34, 0xff, 0x34, 0x34, 0x34, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x20, 0x20, 0x20, 0xff, 0x20, 0x20, 0x20, 0xff, 0x20, 0x20, 0x20, 0xff, 0x20, 0x20, 0x20, 0xff, 0x20, 0x20, 0x20, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x20, 0x20, 0x20, 0xff, 0x20, 0x20, 0x20, 0xff, 0x20, 0x20, 0x20, 0xff, 0x38, 0x38, 0x38, 0xff, 0x48, 0x48, 0x48, 0xff, 0x48, 0x48, 0x48, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x20, 0x20, 0x20, 0xff, 0x20, 0x20, 0x20, 0xff, 0x20, 0x20, 0x20, 0xff, 0x20, 0x20, 0x20, 0xff, 0x20, 0x20, 0x20, 0xff, 0x2c, 0x2c, 0x2c, 0xff, 0x2c, 0x2c, 0x2c, 0xff,
     0x38, 0x38, 0x38, 0xff, 0x54, 0x54, 0x54, 0xff, 0x38, 0x38, 0x38, 0xff, 0x54, 0x54, 0x54, 0xff, 0x38, 0x38, 0x38, 0xff, 0x38, 0x38, 0x38, 0xff, 0x38, 0x38, 0x38, 0xff, 0x48, 0x48, 0x48, 0xff, 0x48, 0x48, 0x48, 0xff, 0x48, 0x48, 0x48, 0xff, 0x48, 0x48, 0x48, 0xff, 0x48, 0x48, 0x48, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x38, 0x38, 0x38, 0xff, 0x48, 0x48, 0x48, 0xff, 0x48, 0x48, 0x48, 0xff, 0x48, 0x48, 0x48, 0xff, 0x48, 0x48, 0x48, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x48, 0x48, 0x48, 0xff, 0x48, 0x48, 0x48, 0xff, 0x48, 0x48, 0x48, 0xff, 0x54, 0x54, 0x54, 0xff, 0x48, 0x48, 0x48, 0xff, 0x48, 0x48, 0x48, 0xff, 0x48, 0x48, 0x48, 0xff, 0x54, 0x54, 0x54, 0xff, 0x48, 0x48, 0x48, 0xff, 0x48, 0x48, 0x48, 0xff, 0x38, 0x38, 0x38, 0xff, 0x48, 0x48, 0x48, 0xff, 0x48, 0x48, 0x48, 0xff, 0x48, 0x48, 0x48, 0xff, 0x40, 0x40, 0x40, 0xff, 0x38, 0x38, 0x38, 0xff, 0x38, 0x38, 0x38, 0xff, 0x40, 0x40, 0x40, 0xff, 0x38, 0x38, 0x38, 0xff, 0x38, 0x38, 0x38, 0xff, 0x40, 0x40, 0x40, 0xff, 0x48, 0x48, 0x48, 0xff, 0x40, 0x40, 0x40, 0xff, 0x38, 0x38, 0x38, 0xff, 0x40, 0x40, 0x40, 0xff, 0x54, 0x54, 0x54, 0xff, 0x48, 0x48, 0x48, 0xff, 0x48, 0x48, 0x48, 0xff, 0x38, 0x38, 0x38, 0xff, 0x54, 0x54, 0x54, 0xff, 0x48, 0x48, 0x48, 0xff, 0x48, 0x48, 0x48, 0xff, 0x48, 0x48, 0x48, 0xff, 0x48, 0x48, 0x48, 0xff, 0x40, 0x40, 0x40, 0xff, 0x38, 0x38, 0x38, 0xff, 0x40, 0x40, 0x40, 0xff, 0x48, 0x48, 0x48, 0xff, 0x48, 0x48, 0x48, 0xff, 0x48, 0x48, 0x48, 0xff,
     0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff, 0x54, 0x54, 0x54, 0xff,
-};
+};
\ No newline at end of file
diff --git a/src/triangle.c b/src/triangle.c
index 668e40f..876dac3 100644
--- a/src/triangle.c
+++ b/src/triangle.c
@@ -1,5 +1,6 @@
 #include "triangle.h"
 #include "display.h"
+#include "vector.h"
 #include "swap.h"
 
 // Draw a filled triangle with a flat bottom
@@ -77,6 +78,78 @@ void draw_filled_triangle(int x0, int y0, int x1, int y1, int x2, int y2, uint32
     }
 }
 
+////////////////////////////////////////////////////////////////////////////////
+// Return the barycentric weights alpha, beta and gamma for point p
+////////////////////////////////////////////////////////////////////////////////
+//
+//          B
+//         /|\
+//        / | \
+//       /  |  \
+//      /  (p)  \
+//     /  /   \  \
+//    /  /     \  \
+//   A-------------C
+//
+////////////////////////////////////////////////////////////////////////////////
+vec3_t barycentric_weights(vec2_t a, vec2_t b, vec2_t c, vec2_t p) {
+    // Find the vectors between the vertices ABC and point p
+    vec2_t ac = vec2_sub(c, a);
+    vec2_t ab = vec2_sub(b, a);
+    vec2_t ap = vec2_sub(p, a);
+    vec2_t pc = vec2_sub(c, p);
+    vec2_t pb = vec2_sub(b, p);
+
+    // Compute the area of the full paralellogram / triangle ABC using 2D cross product
+    float area_parallelogram_abc = (ac.x * ab.y - ac.y * ab.x); // || AC x AB ||
+    
+    // Alpha is the area of the small parallelogram / triangle PBC divided by the area of the full parallelogram / triangle ABC
+    float alpha = (pc.x * pb.y - pc.y * pb.x) / area_parallelogram_abc;
+
+    // Beta is the area of the small parallelogram / triangle APC divided by the area of the ufll parallelogram / triangle ABC
+    float beta = (ac.x * ap.y - ac.y * ap.x) / area_parallelogram_abc;
+
+    // Gamma is found by taking 1 - alpha - beta since barycentric normalized coordinates always add up to 1.0
+    float gamma = 1 - alpha - beta;
+
+    vec3_t weights = { alpha, beta, gamma };
+    return weights;
+}
+
+
+////////////////////////////////////////////////////////////////////////////////
+// Function to draw the textured pixel at position x and y using interpoation
+////////////////////////////////////////////////////////////////////////////////
+void draw_texel(
+        int x, int y, color_t* texture,
+        vec2_t point_a, vec2_t point_b, vec2_t point_c,
+        float u0, float v0, float u1, float v1, float u2, float v2 
+) {
+    vec2_t point_p = { x, y };
+
+    vec3_t weights = barycentric_weights(point_a, point_b, point_c, point_p);
+
+    float alpha = weights.x;
+    float beta = weights.y;
+    float gamma = weights.z;
+   
+    // Perform the interpolation of all the U and V values using barycentric weights (coords) 
+    float interpolated_u = (u0 * alpha) + (u1 * beta) + (u2 * gamma);
+    float interpolated_v = (v0 * alpha) + (v1 * beta) + (v2 * gamma);
+
+    // Map the UV coordinate to the full texture width and height
+    int tex_x = abs((int)(interpolated_u * texture_width));
+    int tex_y = abs((int)(interpolated_v * texture_height));
+
+    // TODO: figure out elegant way for stopping the values of tex_x and tex_y if outside bounds of array to prevent a buffer overflow in the texture[] array
+    if ((texture_width * tex_y) + tex_x >= 0 && (texture_width * tex_y) + tex_x < (texture_width * texture_height)) {
+        draw_pixel(x, y, texture[(texture_width * tex_y) + tex_x]); 
+    } else {
+        //draw_pixel(x, y, 0xFFFFFFFF);
+    }
+}
+
+
 ////////////////////////////////////////////////////////////////////////////////
 // Draw a textured triangle with the flat-top/flat-bottom method
 // We split the original triangle in two, half flat-bottom and half flat-top
@@ -107,7 +180,7 @@ void draw_textured_triangle(
     int x2, int y2, float u2, float v2,
     color_t* texture
 ) {
-    // We need to sort the vertices by y-coordinate asecnding (y0 < y1 < y2)
+    // We need to sort the vertices by y-coordinate ascending (y0 < y1 < y2)
     if (y0 > y1) {
         int_swap(&y0, &y1);
         int_swap(&x0, &x1);
@@ -129,6 +202,11 @@ void draw_textured_triangle(
         float_swap(&v0, &v1);
     }
 
+    // Create vector points after we sort the vertices
+    vec2_t point_a = { x0, y0 };
+    vec2_t point_b = { x1, y1 };
+    vec2_t point_c = { x2, y2 };
+
     //////////////////////////////////////////////////////
     // Render the upper part of the triangle (flat-bottom)
     //////////////////////////////////////////////////////
@@ -150,14 +228,14 @@ void draw_textured_triangle(
 
             for (int x = x_start; x < x_end; x++) {
                 // Draw our pixel with the color that comes from the texture
-                draw_pixel(x, y, 0xFFFF00FF);
+                draw_texel(x, y, texture, point_a, point_b, point_c, u0, v0, u1, v1, u2, v2); 
             }
         }
     }
 
 
     //////////////////////////////////////////////////////
-    // Render the upper part of the triangle (flat-bottom)
+    // Render the bottom part of the triangle (flat-top)
     //////////////////////////////////////////////////////
     inv_slope_1 = 0;
     inv_slope_2 = 0;
@@ -177,7 +255,7 @@ void draw_textured_triangle(
 
             for (int x = x_start; x < x_end; x++) {
                 // Draw our pixel with the color that comes from the texture
-                draw_pixel(x, y, 0xFFFF00FF);
+                draw_texel(x, y, texture, point_a, point_b, point_c, u0, v0, u1, v1, u2, v2); 
             }
         }
     }     
diff --git a/src/triangle.h b/src/triangle.h
index 0403db1..586fa96 100644
--- a/src/triangle.h
+++ b/src/triangle.h
@@ -32,6 +32,10 @@ void draw_textured_triangle(
         color_t* texture 
         );
 
-// TODO: void draw_textured_triangle(...);
+void draw_texel(
+        int x, int y, color_t* texture,
+        vec2_t point_a, vec2_t point_b, vec2_t point_c,
+        float u0, float v0, float u1, float v1, float u2, float v2 
+);
 
 #endif