Rewrite rendering engine (#6253)

* Clean draw_*() arguments

* Split rendering core

* Add anaglyph 3D

* Interlaced 3D

* Drop obsolete methods

client/shaders/3d_interlaced_merge/opengl_fragment.glsl

@@ -0,0 +1,21 @@
+uniform sampler2D baseTexture;
+uniform sampler2D normalTexture;
+uniform sampler2D textureFlags;
+
+#define leftImage baseTexture
+#define rightImage normalTexture
+#define maskImage textureFlags
+
+void main(void)
+{
+	vec2 uv = gl_TexCoord[0].st;
+	vec4 left = texture2D(leftImage, uv).rgba;
+	vec4 right = texture2D(rightImage, uv).rgba;
+	vec4 mask = texture2D(maskImage, uv).rgba;
+	vec4 color;
+	if (mask.r > 0.5)
+		color = right;
+	else
+		color = left;
+	gl_FragColor = color;
+}

client/shaders/3d_interlaced_merge/opengl_vertex.glsl

@@ -0,0 +1,6 @@
+void main(void)
+{
+	gl_TexCoord[0] = gl_MultiTexCoord0;
+	gl_Position = gl_Vertex;
+	gl_FrontColor = gl_BackColor = gl_Color;
+}