From 428f9c360a86cdb2d4921495179f3fc5fdb8c523 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Du=C5=A1an=20Poizl?= <nou.spiro@gmail.com>
Date: Mon, 15 Jan 2024 08:58:14 +0100
Subject: [PATCH] Small optimization in resample

---
 rawimage.cpp | 41 +++++++++++++++++++----------------------
 1 file changed, 19 insertions(+), 22 deletions(-)

diff --git a/rawimage.cpp b/rawimage.cpp
index 1eee356..3234319 100644
--- a/rawimage.cpp
+++ b/rawimage.cpp
@@ -575,43 +575,40 @@ void boxResample(uint32_t w, uint32_t h, uint32_t ch, uint32_t oldw, uint32_t ol
     if constexpr(std::is_same<T, uint16_t>::value)
         max = UINT16_MAX;
 
-    float sx = (float)oldw / w;
-    float sy = (float)oldh / h;
-    float sx_ = (float)w / oldw;
-    float sy_ = (float)h / oldh;
-    float s = 1.0 / (sx * sy);
-    for(uint32_t y = 0; y < h; y++)
+    float sx = (float)w / oldw;
+    float sy = (float)h / oldh;
+    for(uint32_t y = 0; y < h; y++)//iterate over destination Y
     {
-        for(uint32_t x = 0; x < w; x++)
+        for(uint32_t x = 0; x < w; x++)//iterate over destination X
         {
             float p[4] = {0.0f};
-            uint32_t xx = x * oldw / w;
+            uint32_t xx = x * oldw / w;//calculate source rect
             uint32_t yy = y * oldh / h;
             uint32_t xe = std::min((x + 1) * oldw / w, oldw - 1);
             uint32_t ye = std::min((y + 1) * oldh / h, oldh - 1);
-            for(uint32_t o = yy; o <= ye; o++)
+            for(uint32_t o = yy; o <= ye; o++)//iterate over source Y
             {
-                float cy = o * sy_ - y;
-                if(cy < 0.0f)cy = 1.0f + cy * sy;
-                else if(sy_ + cy > 1.0f)cy = (1.0f - cy) * sy;
-                else cy = 1.0f;
-                if(yy==ye)cy = sy;
-                for(uint32_t i = xx; i <= xe; i++)
+                float cy = o * sy - y;
+                if(cy < 0.0f)cy = sy + cy;
+                else if(sy + cy > 1.0f)cy = 1.0f - cy;
+                else cy = sy;
+                if(yy==ye)cy = 1.0f;
+                for(uint32_t i = xx; i <= xe; i++)//iterate over source X
                 {
-                    float cx = i * sx_ - x;
-                    if(cx < 0.0f)cx = 1.0f + cx * sx;
-                    else if(sx_ + cx > 1.0f)cx = (1.0f - cx) * sx;
-                    else cx = 1.0f;
-                    if(xx==xe)cx = sx;
+                    float cx = i * sx - x;
+                    if(cx < 0.0f)cx = sx + cx;
+                    else if(sx + cx > 1.0f)cx = 1.0f - cx;
+                    else cx = sx;
+                    if(xx==xe)cx = 1.0f;
                     for(uint32_t z = 0; z < ch; z++)
                         p[z] += in[(o * oldw + i) * ch + z] * cy * cx;
                 }
             }
             for(uint32_t z = 0; z < ch; z++)
                 if constexpr(std::is_floating_point<T>::value)
-                    out[(y * w + x) * ch + z] = p[z] * s;
+                    out[(y * w + x) * ch + z] = p[z];
                 else
-                    out[(y * w + x) * ch + z] = std::clamp(std::round(p[z] * s), 0.0f, max);
+                    out[(y * w + x) * ch + z] = std::clamp(std::round(p[z]), 0.0f, max);
         }
     }
 }