Port shadow shaders to work with OpenGL3

Co-authored-by: sfan5 <sfan5@live.de>

client/shaders/shadow/pass1/opengl_fragment.glsl

@@ -0,0 +1,19 @@
+uniform sampler2D ColorMapSampler;
+varying vec4 tPos;
+
+#ifdef GL_ES
+varying mediump vec2 varTexCoord;
+#else
+centroid varying vec2 varTexCoord;
+#endif
+
+void main()
+{
+	vec4 col = texture2D(ColorMapSampler, varTexCoord);
+
+	if (col.a < 0.70)
+		discard;
+
+	float depth = 0.5 + tPos.z * 0.5;
+	gl_FragColor = vec4(depth, 0.0, 0.0, 1.0);
+}

client/shaders/shadow/pass1/opengl_vertex.glsl

@@ -0,0 +1,49 @@
+uniform mat4 LightMVP; // world matrix
+uniform vec4 CameraPos; // camera position
+varying vec4 tPos;
+
+uniform float xyPerspectiveBias0;
+uniform float xyPerspectiveBias1;
+uniform float zPerspectiveBias;
+
+#ifdef GL_ES
+varying mediump vec2 varTexCoord;
+#else
+centroid varying vec2 varTexCoord;
+#endif
+
+vec4 getRelativePosition(in vec4 position)
+{
+	vec2 l = position.xy - CameraPos.xy;
+	vec2 s = l / abs(l);
+	s = (1.0 - s * CameraPos.xy);
+	l /= s;
+	return vec4(l, s);
+}
+
+float getPerspectiveFactor(in vec4 relativePosition)
+{
+	float pDistance = length(relativePosition.xy);
+	float pFactor = pDistance * xyPerspectiveBias0 + xyPerspectiveBias1;
+	return pFactor;
+}
+
+vec4 applyPerspectiveDistortion(in vec4 position)
+{
+	vec4 l = getRelativePosition(position);
+	float pFactor = getPerspectiveFactor(l);
+	l.xy /= pFactor;
+	position.xy = l.xy * l.zw + CameraPos.xy;
+	position.z *= zPerspectiveBias;
+	return position;
+}
+
+void main()
+{
+	vec4 pos = LightMVP * inVertexPosition;
+
+	tPos = applyPerspectiveDistortion(pos);
+
+	gl_Position = vec4(tPos.xyz, 1.0);
+	varTexCoord = (mTexture * vec4(inTexCoord0.xy, 0.0, 1.0)).xy;
+}