Shadow mapping render pass (#11244)

Co-authored-by: x2048 <codeforsmile@gmail.com>

client/shaders/shadow_shaders/pass1_vertex.glsl

@@ -0,0 +1,26 @@
+uniform mat4 LightMVP; // world matrix
+varying vec4 tPos;
+
+const float bias0 = 0.9;
+const float zPersFactor = 0.5;
+const float bias1 = 1.0 - bias0 + 1e-6;
+
+vec4 getPerspectiveFactor(in vec4 shadowPosition)
+{
+	float pDistance = length(shadowPosition.xy);
+	float pFactor = pDistance * bias0 + bias1;
+	shadowPosition.xyz *= vec3(vec2(1.0 / pFactor), zPersFactor);
+
+	return shadowPosition;
+}
+
+
+void main()
+{
+	vec4 pos = LightMVP * gl_Vertex;
+
+	tPos = getPerspectiveFactor(pos);
+
+	gl_Position = vec4(tPos.xyz, 1.0);
+	gl_TexCoord[0].st = gl_MultiTexCoord0.st;
+}