From 2a5dcfb26f536d705a8f71548b24b2262ca7715e Mon Sep 17 00:00:00 2001
From: Mistivia <i@mistivia.com>
Date: Tue, 10 Jun 2025 07:33:35 +0800
Subject: anti alias

---
 Makefile      |  2 +-
 src/main.c    |  8 +++++---
 src/picture.c | 20 ++++++++++++++++++++
 src/picture.h |  1 +
 src/vecmath.c | 10 ++++++++++
 src/vecmath.h |  2 ++
 6 files changed, 39 insertions(+), 4 deletions(-)

diff --git a/Makefile b/Makefile
index 402d621..5009f17 100644
--- a/Makefile
+++ b/Makefile
@@ -1,2 +1,2 @@
 all:
-	gcc -g -fsanitize=address -lm src/*.c -o main 
+	gcc -O2 -flto -lm src/*.c -o main 
diff --git a/src/main.c b/src/main.c
index 6e37e37..71ced79 100644
--- a/src/main.c
+++ b/src/main.c
@@ -143,8 +143,8 @@ Color calc_color(Vec3f v) {
 
 int main() {
     init_color();
-    int img_w = 1280;
-    int img_h = 720;
+    int img_w = 1280*2;
+    int img_h = 720*2;
     Picture pic = new_picture(img_w, img_h);
     for (int x = 0; x < img_w; x++) {
         for (int y = 0; y < img_h; y++) {
@@ -153,8 +153,10 @@ int main() {
             set_pixel(pic, screen_pos, calc_color(v));
         }
     }
-    writeBMP("test.bmp", pic);
+    Picture newpic = picture_downscale_2x(pic);
+    writeBMP("test.bmp", newpic);
     delete_picture(pic);
+    delete_picture(newpic);
     return 0;
 }
 
diff --git a/src/picture.c b/src/picture.c
index 52deb0e..ebb1fec 100644
--- a/src/picture.c
+++ b/src/picture.c
@@ -17,6 +17,11 @@ void delete_picture(Picture pic) {
     free(pic.buffer);
 }
 
+Color get_pixel(Picture pic, Vec2i pos) {
+    int idx = pos.y * pic.width * 3 + pos.x * 3;
+    return (Color) { pic.buffer[idx+2], pic.buffer[idx+1], pic.buffer[idx] };
+}
+
 void set_pixel(Picture pic, Vec2i pos, Color c) {
     int idx = pos.y * pic.width * 3 + pos.x * 3;
     pic.buffer[idx] = c.b;
@@ -37,6 +42,21 @@ void normalize_picture(Picture pic) {
     }
 }
 
+Picture picture_downscale_2x(Picture pic) {
+    Picture newpic = new_picture(pic.width / 2, pic.height / 2);
+    for (int x = 0; x < newpic.width; x++) {
+        for (int y = 0; y < newpic.height; y++) {
+            Color pixels[4];
+            pixels[0] = get_pixel(pic, (Vec2i){2*x, 2*y});
+            pixels[1] = get_pixel(pic, (Vec2i){2*x+1, 2*y});
+            pixels[2] = get_pixel(pic, (Vec2i){2*x, 2*y+1});
+            pixels[3] = get_pixel(pic, (Vec2i){2*x+1, 2*y+1});
+            set_pixel(newpic, (Vec2i){x,y}, pixel_avg4(pixels));
+        }
+    }
+    return newpic;
+}
+
 
 static bool fwrite_word16le(FILE* fp, uint16_t x) {
     uint8_t buf[2];
diff --git a/src/picture.h b/src/picture.h
index fec5d36..5e50926 100644
--- a/src/picture.h
+++ b/src/picture.h
@@ -17,6 +17,7 @@ void delete_picture(Picture pic);
 
 void set_pixel(Picture pic, Vec2i pos, Color c);
 void normalize_picture(Picture pic);
+Picture picture_downscale_2x(Picture pic);
 
 bool writeBMP(const char* filename, Picture pic);
 
diff --git a/src/vecmath.c b/src/vecmath.c
index 8f1c43d..c3230f6 100644
--- a/src/vecmath.c
+++ b/src/vecmath.c
@@ -46,3 +46,13 @@ Color icolor(int32_t rgb) {
 void vec3f_show(const char *name, Vec3f v) {
     printf("%s(%f,%f,%f)\n", name, v.x, v.y, v.z);
 }
+
+Color pixel_avg4(Color pixels[4]) {
+    float r = 0,g = 0,b = 0;
+    for (int i = 0; i < 4; i++) {
+        r += pixels[i].r; 
+        g += pixels[i].g; 
+        b += pixels[i].b; 
+    }
+    return (Color) {r/4.0, g/4.0, b/4.0};
+}
diff --git a/src/vecmath.h b/src/vecmath.h
index 3b6f5b6..c797b94 100644
--- a/src/vecmath.h
+++ b/src/vecmath.h
@@ -28,6 +28,8 @@ Vec3f vec3f_neg(Vec3f v);
 Vec3f vec3f_normalize(Vec3f vec);
 Vec3f vec3f_mul(float a, Vec3f v);
 void vec3f_show(const char *name, Vec3f v);
+
 Color icolor(int32_t rgb);
+Color pixel_avg4(Color pixels[4]);
 
 #endif
-- 
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