build preview update

Shaders/build_transparent.gdshader

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+shader_type spatial;
+uniform float alpha;
+void vertex() {
+	// Called for every vertex the material is visible on.
+}
+
+void fragment() {
+	ALBEDO = vec3(0,1.0,0);
+	ALPHA = alpha;
+}
+
+//void light() {
+//	// Called for every pixel for every light affecting the material.
+//	// Uncomment to replace the default light processing function with this one.
+//}