shaderlib: Add alpha_blend function, extend place_texture example, update autocomplete - implements #23

examples/place_texture.gdshader

@@ -1,6 +1,7 @@
 shader_type canvas_item;
 
 #include "res://shaderlib/transform.gdshaderinc"
+#include "res://shaderlib/transparency.gdshaderinc"
 
 //!load ./swamp.jpg
 //!load+ img2 ./grass.png
@@ -9,6 +10,6 @@ uniform sampler2D img2: repeat_disable, filter_nearest;
 
 void fragment() {
 	vec4 grass = place_texture(img2, UV, TEXTURE_PIXEL_SIZE, vec2(0, .47), vec2(1));
-	grass.rgb += (vec3(0.03, 0.07, 0.11) - ((UV.y - .8) * 0.15)); // color correction
-	COLOR.rgb = mix(COLOR.rgb, grass.rgb, grass.a);
+	grass.rgb += (vec3(0.02, 0.07, 0.1) - ((UV.y - .8) * 0.15)); // color correction
+	COLOR = alpha_blend(COLOR, grass);
 }