Fix support for GLES2

uints don't work in GLES2, so just strip out the phasing effect for the
shader if we encounter GLES2

addons/MagicaVoxelImporter/VoxelMesh.gd

@@ -8,6 +8,24 @@ export(float, 0.0, 1.0) var phase_shift setget _set_phase_shift
 func _ready():
 	_set_neck_height(neck_height)
 	_set_render_head(true)
+	if OS.get_current_video_driver() == OS.VIDEO_DRIVER_GLES2:
+		_strip_gles3_from_shader()
+
+
+func _strip_gles3_from_shader():
+	if Engine.editor_hint:
+		return
+	var mat = mesh.surface_get_material(0) as ShaderMaterial
+	if !mat || mat.shader.has_meta('gles3_stripped'):
+		return
+	var strip_expr = RegEx.new()
+	strip_expr.compile("(?s)\\/\\/ #ifndef GLES3.+?\\/\\/ #endif")
+	var code = mat.shader.code
+	var stripped_code = strip_expr.sub(code, '', true)
+	if code != stripped_code:
+		mat.shader.code = stripped_code
+		mat.shader.set_meta('gles3_stripped', true)
+
 
 func _get_mats() -> Array:
 	var result = []

addons/MagicaVoxelImporter/points.shader

@@ -26,10 +26,13 @@ uniform float lod_bias = 1.0;
 // limiting this is somehow faster than allowing the whole mesh to be discarded.
 uniform float lod_worst = 5.0;
 // multiply a uint by this number to get a range from 0 .. 2.0
+// #ifndef GLES3
 const float MAX_UINT_INV_2 = 2.0 / float(~0u);
+// #endif
 const float PHASE_TRANSLATE = 0.01;
 const float PHASE_SHRINK = 0.25;
 
+// #ifndef GLES3
 uint pcg_hash(uint input) {
 	// https://www.reedbeta.com/blog/hash-functions-for-gpu-rendering/
     uint state = input * 747796405u + 2891336453u;
@@ -53,7 +56,7 @@ vec3 phase_shift_vertex(vec3 value, float amount) {
 		phase_shift_component(value.z + value.y + amount, value.z, amount)
 	);
 }
-
+// #endif
 
 void vertex() {
 	if (!render_head && VERTEX.y > neck_height) {
@@ -143,13 +146,14 @@ void vertex() {
 				mod(VERTEX.x, reduction) >= 1.0 && mod(VERTEX.y, reduction) >= 1.0 && mod(VERTEX.z + 1.0, reduction) >= 1.0
 			) {
 				voxel_size = vec2(0.0);
-const uint MAX_UINT = ~0u;
 			}
 		}
+		// #ifndef GLES3
 		if (phase_shift > 0.0) {
 			VERTEX = phase_shift_vertex(VERTEX, phase_shift * voxel_size.x * PHASE_TRANSLATE);
 			voxel_size *= 1.0 - phase_shift * (1.0 - PHASE_SHRINK);
 		}
+		// #endif
 		POINT_SIZE = max(voxel_size.x, voxel_size.y);
 
 		if (show_normals > 0.0) {