Add instancing grass demo

res/org/lwjgl/demo/opengl/instancing/CREDITS

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+The following textures are made by Reiner Prokein and can be found on [http://www.reinerstilesets.de/new-textures-billboard-grass/]:
+- grass_flower_blue.png
+- grass_flower.png
+- grass.png
+- grass2.png

res/org/lwjgl/demo/opengl/instancing/grass.fs

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+/*
+ * Copyright LWJGL. All rights reserved.
+ * License terms: http://lwjgl.org/license.php
+ */
+#version 110
+
+uniform sampler2D tex0;
+uniform sampler2D tex1;
+uniform sampler2D tex2;
+uniform sampler2D tex3;
+
+varying vec2 texCoordVarying;
+varying float yVarying;
+varying vec3 normalVarying;
+varying float texIndexVarying;
+
+const vec3 LIGHT_DIR = normalize(vec3(0.1, 1, 0.1));
+
+void main(void) {
+  vec3 n = normalize(normalVarying);
+  float dot = max(0.0, dot(LIGHT_DIR, n));
+  vec4 col;
+  int texIndexVaryingI = int(texIndexVarying);
+  if (texIndexVaryingI == 0)
+    col = texture2D(tex0, texCoordVarying);
+  else if (texIndexVaryingI == 1)
+    col = texture2D(tex1, texCoordVarying);
+  else if (texIndexVaryingI == 2)
+    col = texture2D(tex2, texCoordVarying);
+  else
+    col = texture2D(tex3, texCoordVarying);
+  col.rgb *= yVarying;
+  if (col.a < 0.8)
+    discard;
+  gl_FragColor = vec4(col.rgb * dot, col.a);
+}

res/org/lwjgl/demo/opengl/instancing/grass.vs

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+/*
+ * Copyright LWJGL. All rights reserved.
+ * License terms: http://lwjgl.org/license.php
+ */
+#version 110
+#extension GL_NV_non_square_matrices : enable
+
+attribute vec3 position;
+attribute vec2 texCoord;
+attribute vec2 displacement;
+attribute vec4 worldPosition;
+attribute vec4 rotation;
+
+uniform mat4 vpMatrix;
+
+varying vec2 texCoordVarying;
+varying float yVarying;
+varying vec3 normalVarying;
+varying float texIndexVarying;
+
+void main(void) {
+  texCoordVarying = texCoord;
+  texIndexVarying = worldPosition.w * worldPosition.w * 4.0;
+  yVarying = position.y;
+  vec3 spos = position;
+  spos.y *= worldPosition.z;
+  vec2 pos = spos.xz;
+  mat2x2 rot = mat2x2(rotation.x, rotation.y, rotation.z, rotation.w);
+  pos = rot * pos;
+  pos += displacement * yVarying;
+  pos += worldPosition.xy;
+  normalVarying = vec3(0.0, 1.0, 0.0);
+  normalVarying.xz += displacement * yVarying;
+  gl_Position = vpMatrix * vec4(pos.x, spos.y, pos.y, 1.0);
+}

res/org/lwjgl/demo/opengl/instancing/ground.fs

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+/*
+ * Copyright LWJGL. All rights reserved.
+ * License terms: http://lwjgl.org/license.php
+ */
+#version 110
+
+void main(void) {
+  gl_FragColor = vec4(0.2, 0.2, 0.13, 1.0);
+}

res/org/lwjgl/demo/opengl/instancing/ground.vs

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+/*
+ * Copyright LWJGL. All rights reserved.
+ * License terms: http://lwjgl.org/license.php
+ */
+#version 110
+
+attribute vec2 position;
+
+uniform mat4 vpMatrix;
+uniform float groundSize;
+
+varying vec2 texCoordVarying;
+
+void main(void) {
+  texCoordVarying = position * groundSize;
+  vec2 pos = position * 2.0 - vec2(1.0, 1.0);
+  pos *= groundSize;
+  gl_Position = vpMatrix * vec4(pos.x, 0.0, pos.y, 1.0);
+}