From 6ce19277e54e0c56be105d8edac118aa3f41ba67 Mon Sep 17 00:00:00 2001
From: Ulysse Cura <ulysse.cura@gmail.com>
Date: Tue, 1 Sep 2026 17:29:56 +0200
Subject: [PATCH] Added linear interpolation with time.

---
 src/Makefile           |  2 +-
 src/headers/vector2d.h | 20 +++++++++++++++++++-
 src/vector2d.c         |  9 +++++++--
 3 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/src/Makefile b/src/Makefile
index d362217..67f7bcb 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -34,7 +34,7 @@ CORE_AR = ar
 CORE_ARFLAGS =
 
 # Used in final linking.
-CORE_DEPS_FLAGS = $(shell pkg-config --libs sdl3)
+CORE_DEPS_FLAGS = $(shell pkg-config --libs sdl3) -lm
 
 # Deduce objects
 CORE_OBJECTS = $(CORE_SOURCES:%.c=$(BUILD_DIR)/$(CORE_DIR)/%.o)
diff --git a/src/headers/vector2d.h b/src/headers/vector2d.h
index bfb45b4..ab511b8 100644
--- a/src/headers/vector2d.h
+++ b/src/headers/vector2d.h
@@ -130,6 +130,24 @@ void frect_to_rect(const frect_t *frect, rect_t *rect);
 */
 #define intersect_frect(A, B, result) SDL_GetRectIntersectionFloat(A, B, result)
 
-float lerp(float a, float b, float t);
+/**
+ * @brief Lerp a to b with smoothing factor s.
+ *
+ * @param a Current value
+ * @param b Target value
+ * @param s Smoothing factor
+ */
+float lerp(float a, float b, float s);
+
+/**
+ * @brief Lerp a to b with smoothing factor s and time basis t.
+ * Smoothing factor is for 60 fps call time.
+ *
+ * @param a Current value
+ * @param b Target value
+ * @param s Smoothing factor
+ * @param t Delta time
+ */
+float lerp_time(float a, float b, float s, float t);
 
 #endif // VECTOR2D_H
\ No newline at end of file
diff --git a/src/vector2d.c b/src/vector2d.c
index 71d8be0..d52ae03 100644
--- a/src/vector2d.c
+++ b/src/vector2d.c
@@ -16,7 +16,12 @@ void frect_to_rect(const frect_t *frect, rect_t *rect)
     rect->h = (int)frect->h;
 }
 
-float lerp(float a, float b, float t)
+inline float lerp(float a, float b, float s)
 {
-    return a * (1 - t) + b * t;
+    return a * (1 - s) + b * s;
 }
+
+inline float lerp_time(float a, float b, float s, float t)
+{
+    return lerp(a, b, 1 - powf(1 - s, t * 60.0f));
+}
\ No newline at end of file