From 86f8f4fec9e71d541ceb707788cd282a370d6b7c Mon Sep 17 00:00:00 2001
From: Bruno BELANYI <bruno@belanyi.fr>
Date: Tue, 10 Nov 2020 17:39:00 +0100
Subject: [PATCH] add helper function to compute pixel indices

---
 src/image.h | 4 ++++
 src/main.c  | 2 +-
 src/ppm.c   | 2 +-
 3 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/image.h b/src/image.h
index 6b94d52..3ee7d17 100644
--- a/src/image.h
+++ b/src/image.h
@@ -16,4 +16,8 @@ struct image {
 struct image *create_image(size_t w, size_t h);
 void destroy_image(struct image *image);
 
+static inline size_t to_index(size_t h, size_t w, const struct image *image) {
+    return h * image->w + w;
+}
+
 #endif /* !IMAGE_H */
diff --git a/src/main.c b/src/main.c
index d83f1b7..1695c83 100644
--- a/src/main.c
+++ b/src/main.c
@@ -9,7 +9,7 @@
 static void fill_image(struct image *image) {
     for (size_t i = 0; i < image->h; ++i) {
         for (size_t j = 0; j < image->w; ++j) {
-            struct pixel *p = &image->buf[i * image->w + j];
+            struct pixel *p = &image->buf[to_index(i, j, image)];
             p->r = 255 * i / image->h;
             p->g = 255 * j / image->w;
             p->g = 255 * (i + j) / (image->h + image->w);
diff --git a/src/ppm.c b/src/ppm.c
index 5696c18..bb0a368 100644
--- a/src/ppm.c
+++ b/src/ppm.c
@@ -14,7 +14,7 @@ void print_ppm(const struct image *image, FILE *f) {
         for (size_t j = 0; j < image->w; ++j) {
             if (j != 0)
                 fputc(' ', f);
-            const struct pixel *p = &image->buf[i * image->w + j];
+            const struct pixel *p = &image->buf[to_index(i, j, image)];
             fprintf(f, "%hhu %hhu %hhu", p->r, p->g, p->b);
         }
         fputc('\n', f);