feat(track): parallax track materials blended at the joints

shaders/mat_trackblend_parallax.frag

@@ -0,0 +1,22 @@
+// the rails of a track of a parallax material faded into those of the tracks joined at its ends, see trackblend.glsl
+#define TRACKBLEND_NORMALMAP 1
+#define TRACKBLEND_PARALLAX 1
+#param (height_scale, 2, 1, 1, zero)
+#param (height_offset, 2, 2, 1, zero)
+#texture (diffuse, 0, sRGB_A)
+uniform sampler2D diffuse;
+#texture (diffuse1, 1, sRGB_A)
+uniform sampler2D diffuse1;
+#texture (diffuse2, 2, sRGB_A)
+uniform sampler2D diffuse2;
+#texture (diffuse3, 3, sRGB_A)
+uniform sampler2D diffuse3;
+#texture (normalmap, 4, RGBA)
+uniform sampler2D normalmap;
+#texture (normalmap1, 5, RGBA)
+uniform sampler2D normalmap1;
+#texture (normalmap2, 6, RGBA)
+uniform sampler2D normalmap2;
+#texture (normalmap3, 7, RGBA)
+uniform sampler2D normalmap3;
+#include <trackblend.glsl>