From 8e221cbc89e523a60f4ff9915b94ad7abeef844b Mon Sep 17 00:00:00 2001
From: "Dmitry V. Sokolov" <ha@haqr.eu>
Date: Sat, 9 Feb 2019 17:05:45 +0100
Subject: [PATCH] apply textures to the walls

---
 tinyraycaster.cpp | 34 +++++++++++++++++++++++++++++++---
 1 file changed, 31 insertions(+), 3 deletions(-)

diff --git a/tinyraycaster.cpp b/tinyraycaster.cpp
index 10ee09f..8ed98a2 100644
--- a/tinyraycaster.cpp
+++ b/tinyraycaster.cpp
@@ -79,6 +79,18 @@ bool load_texture(const std::string filename, std::vector<uint32_t> &texture, si
     return true;
 }
 
+std::vector<uint32_t> texture_column(const std::vector<uint32_t> &img, const size_t texsize, const size_t ntextures, const size_t texid, const size_t texcoord, const size_t column_height) {
+    const size_t img_w = texsize*ntextures;
+    const size_t img_h = texsize;
+    assert(img.size()==img_w*img_h && texcoord<texsize && texid<ntextures);
+    std::vector<uint32_t> column(column_height);
+    for (size_t y=0; y<column_height; y++) {
+        size_t pix_x = texid*texsize + texcoord;
+        size_t pix_y = (y*texsize)/column_height;
+        column[y] = img[pix_x + pix_y*img_w];
+    }
+    return column;
+}
 
 int main() {
     const size_t win_w = 1024; // image width
@@ -136,15 +148,31 @@ int main() {
             float cx = player_x + t*cos(angle);
             float cy = player_y + t*sin(angle);
 
-            size_t pix_x = cx*rect_w;
-            size_t pix_y = cy*rect_h;
+            int pix_x = cx*rect_w;
+            int pix_y = cy*rect_h;
             framebuffer[pix_x + pix_y*win_w] = pack_color(160, 160, 160); // this draws the visibility cone
 
             if (map[int(cx)+int(cy)*map_w]!=' ') { // our ray touches a wall, so draw the vertical column to create an illusion of 3D
                 size_t texid = map[int(cx)+int(cy)*map_w] - '0';
                 assert(texid<walltext_cnt);
                 size_t column_height = win_h/(t*cos(angle-player_a));
-                draw_rectangle(framebuffer, win_w, win_h, win_w/2+i, win_h/2-column_height/2, 1, column_height, walltext[texid*walltext_size]);
+
+                float hitx = cx - floor(cx+.5); // hitx and hity contain (signed) fractional parts of cx and cy,
+                float hity = cy - floor(cy+.5); // they vary between -0.5 and +0.5, and one of them is supposed to be very close to 0
+                int x_texcoord = hitx*walltext_size;
+                if (std::abs(hity)>std::abs(hitx)) { // we need to determine whether we hit a "vertical" or a "horizontal" wall (w.r.t the map)
+                    x_texcoord = hity*walltext_size;
+                }
+                if (x_texcoord<0) x_texcoord += walltext_size; // do not forget x_texcoord can be negative, fix that
+                assert(x_texcoord>=0 && x_texcoord<(int)walltext_size);
+
+                std::vector<uint32_t> column = texture_column(walltext, walltext_size, walltext_cnt, texid, x_texcoord, column_height);
+                pix_x = win_w/2+i;
+                for (size_t j=0; j<column_height; j++) {
+                    pix_y = j + win_h/2-column_height/2;
+                    if (pix_y<0 || pix_y>=(int)win_h) continue;
+                    framebuffer[pix_x + pix_y*win_w] = column[j];
+                }
                 break;
             }
         }