From 7c5a6166d8f48c7cb6848a103a4d7de7e21dcf75 Mon Sep 17 00:00:00 2001
From: Dan Goodliffe <dan@randomdan.homeip.net>
Date: Thu, 25 Nov 2021 00:35:04 +0000
Subject: Add slope colouring to terrain shader

---
 gfx/gl/shaders/landmassShader.fs | 48 ++++++++++++++++++++++++++++++++--------
 1 file changed, 39 insertions(+), 9 deletions(-)

(limited to 'gfx/gl')

diff --git a/gfx/gl/shaders/landmassShader.fs b/gfx/gl/shaders/landmassShader.fs
index 09e4565..ee943d7 100644
--- a/gfx/gl/shaders/landmassShader.fs
+++ b/gfx/gl/shaders/landmassShader.fs
@@ -10,6 +10,8 @@ uniform vec3 lightColor;
 uniform vec3 ambientColor;
 
 const vec3 grass = vec3(.1, .4, .05);
+const vec3 slope = vec3(.6, .6, .4);
+const vec3 rock = vec3(.2, .2, .1);
 const vec3 sand = vec3(.76, .7, .5);
 const vec3 snow = vec3(.97, .97, .99);
 
@@ -17,21 +19,49 @@ const float beachline = .5;
 const float snowline_low = 28;
 const float snowline_high = 30;
 
+const float slope_min = .99;
+const float slope_mid = .95;
+const float slope_max = .90;
+
+vec3
+mixBetween(vec3 colA, vec3 colB, float blend, float low, float high)
+{
+	return mix(colA, colB, (blend - low) / (high - low));
+}
+
 void
 main()
 {
-	gl_FragColor = texture(sampler, texCoord0);
+	vec4 tex = texture(sampler, texCoord0);
+	gl_FragColor = tex;
 	gl_FragColor.rgb *= clamp(ambientColor + (dot(-lightDirection, normal0) * lightColor), 0.0, 1.0);
-	if (height < beachline) {
+
+	if (height < beachline) { // Sandy beach
 		gl_FragColor.rgb *= sand;
 	}
-	else if (height > snowline_high) {
-		gl_FragColor.rgb *= snow;
-	}
-	else if (height > snowline_low) {
-		gl_FragColor.rgb *= mix(grass, snow, (height - snowline_low) / (snowline_high - snowline_low));
+	else if (normal0.z < slope_max) { // Dark rocky face
+		gl_FragColor.rgb *= rock;
 	}
-	else {
-		gl_FragColor.rgb *= grass;
+	else { // Colour by lesser slope
+		if (normal0.z < slope_mid) {
+			gl_FragColor.rgb *= mixBetween(rock, slope, normal0.z, slope_max, slope_mid);
+		}
+		else if (normal0.z < slope_min) {
+			gl_FragColor.rgb *= mixBetween(slope, grass, normal0.z, slope_mid, slope_min);
+		}
+		else {
+			gl_FragColor.rgb *= grass;
+		}
+
+		// Add a snow covering
+		if (height > snowline_low) {
+			vec3 tsnow = tex.rgb * snow;
+			if (height > snowline_high) {
+				gl_FragColor.rgb = tsnow;
+			}
+			else {
+				gl_FragColor.rgb = mixBetween(gl_FragColor.rgb, tsnow, height, snowline_low, snowline_high);
+			}
+		}
 	}
 }
-- 
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