From 136a7fcbfabb2f0b0b3e340213e36a548715a370 Mon Sep 17 00:00:00 2001
From: Eleni Maria Stea <estea@igalia.com>
Date: Sun, 20 Aug 2017 23:56:12 +0300
Subject: [PATCH] added linear interpolation in image to use it at the terrain
 generation

---
 src/image.cc   |   41 +++++++++++++++++++++++++++++++++++++----
 src/image.h    |    4 +++-
 src/terrain.cc |    2 +-
 3 files changed, 41 insertions(+), 6 deletions(-)

diff --git a/src/image.cc b/src/image.cc
index a99f75a..82d8cd1 100644
--- a/src/image.cc
+++ b/src/image.cc
@@ -121,11 +121,8 @@ bool Image::load(const char *fname)
 	return true;
 }
 
-Vec4 Image::lookup_nearest(float u, float v) const
+Vec4 Image::get_pixel(int x, int y) const
 {
-	int x = (int)(u * w) % w;
-	int y = (int)(v * h) % h;
-
 	if(is_float) {
 		return ((Vec4*)pixels)[y * w + x];
 	}
@@ -138,4 +135,40 @@ Vec4 Image::lookup_nearest(float u, float v) const
 	color.w = pptr[3] / 255.0;
 
 	return color;
+}
+
+Vec4 Image::lookup_nearest(float u, float v) const
+{
+	int x = (int)(u * w) % w;
+	int y = (int)(v * h) % h;
+
+	return get_pixel(x, y);
+}
+
+Vec4 Image::lookup_linear(float u, float v, float du, float dv) const
+{
+	/* bottom left */
+	int x0 = (int)(u * w) % w;
+	int y0 = (int)(v * h) % h;
+	int x1 = (x0 + 1) % w;
+	int y1 = (y0 + 1) % h;
+
+	/* uv coordinates at the img corners */
+	float u0 = (float)x0 / (float)w;
+	float v0 = (float)y0 / (float)h;
+	float u1 = (float)(x0 + 1) / (float)w;
+	float v1 = (float)(y0 + 1) / (float)h;
+
+	float tu = (u - u0) / (u1 - u0);
+	float tv = (v - v0) / (v1 - v0);
+
+	Vec4 p00 = get_pixel(x0, y0);
+	Vec4 p01 = get_pixel(x0, y1);
+	Vec4 p11 = get_pixel(x1, y1);
+	Vec4 p10 = get_pixel(x1, y0); 
+
+	Vec4 ptop = lerp(p01, p11, tu);
+	Vec4 pbot = lerp(p00, p10, tu);
+
+	return lerp(pbot, ptop, tv);
 }
\ No newline at end of file
diff --git a/src/image.h b/src/image.h
index ec5228d..3f3ba54 100644
--- a/src/image.h
+++ b/src/image.h
@@ -27,8 +27,10 @@ public:
 
 	bool load(const char *fname);
 
+	Vec4 get_pixel(int x, int y) const;
+
 	Vec4 lookup_nearest(float u, float v) const;
-	//TODO lookup_linear
+	Vec4 lookup_linear(float u, float v, float du, float dv) const;
 };
 
 #endif // IMAGE_H_
\ No newline at end of file
diff --git a/src/terrain.cc b/src/terrain.cc
index c4db7ed..0f10074 100644
--- a/src/terrain.cc
+++ b/src/terrain.cc
@@ -115,7 +115,7 @@ float Terrain::get_height(float u, float v) const
 	sn = sn * 0.5 + 0.5;
 
 	if(params.coarse_heightmap.pixels) {
-		Vec4 texel = params.coarse_heightmap.lookup_nearest(u, v);
+		Vec4 texel = params.coarse_heightmap.lookup_linear(u, v, 1.0 / params.tile_usub, 1.0 / params.tile_vsub);
 		sn *= texel.x;
 	}
 	return sn;
-- 
1.7.10.4