shaderlib: Implement place_texture() and provide an example, replace mix.gdshader example; implements #17

README.md

@@ -31,18 +31,22 @@ The image file will be read and available as the `TEXTURE` variable.
 uniform sampler2D <name>;
 ```
 
-Have a look at the `mix.gdshader` example:
+Have a look at the `place_texture.gdshader` example:
 
 ```glsl
 shader_type canvas_item;
 
-//!load ./swamp.jpg
+#include "res://shaderlib/transform.gdshaderinc"
 
-//!load+ img2 ./overlay.jpg
-uniform sampler2D img2: repeat_enable, filter_nearest;
+//!load ./swamp.jpg
+//!load+ img2 ./grass.png
+
+uniform sampler2D img2: repeat_disable, filter_nearest;
 
 void fragment() {
-	COLOR = mix(COLOR, texture(img2, UV), .2);
+	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);
 }
 ```
 

examples/CREDITS.md

@@ -1,5 +1,5 @@
 
 # Example Images
 
-- swamp.jpg by [clfr21](https://pixabay.com/de/users/clfr21-6530007/)
-- overlay.jpg by [Humusak](https://pixabay.com/de/users/humusak-137455/)
+- swamp.jpg by [clfr21 on Pixabay](https://pixabay.com/de/users/clfr21-6530007/)
+- grass.png by [GDJ on Pixabay](https://pixabay.com/users/gdj-1086657/)

examples/grass.png.import

@@ -2,16 +2,16 @@
 
 importer="texture"
 type="CompressedTexture2D"
-uid="uid://8101nnc8cx4o"
-path="res://.godot/imported/overlay.jpg-b6d13e0def59877969c9eda02fa4244e.ctex"
+uid="uid://c1mh1d2f3u4ju"
+path="res://.godot/imported/grass.png-30af7213ed2d70b810b4ae788314a9e9.ctex"
 metadata={
 "vram_texture": false
 }
 
 [deps]
 
-source_file="res://examples/overlay.jpg"
-dest_files=["res://.godot/imported/overlay.jpg-b6d13e0def59877969c9eda02fa4244e.ctex"]
+source_file="res://examples/grass.png"
+dest_files=["res://.godot/imported/grass.png-30af7213ed2d70b810b4ae788314a9e9.ctex"]
 
 [params]
 

examples/mix.gdshader

@@ -1,10 +0,0 @@
-shader_type canvas_item;
-
-//!load ./swamp.jpg
-
-//!load+ img2 ./overlay.jpg
-uniform sampler2D img2: repeat_enable, filter_nearest;
-
-void fragment() {
-	COLOR = mix(COLOR, texture(img2, UV), .2);
-}

examples/place_texture.gdshader

@@ -0,0 +1,14 @@
+shader_type canvas_item;
+
+#include "res://shaderlib/transform.gdshaderinc"
+
+//!load ./swamp.jpg
+//!load+ img2 ./grass.png
+
+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);
+}

shaderlib/transform.gdshaderinc

@@ -0,0 +1,19 @@
+
+// Load in a texture from a sampler2D with an offset and scale
+// See examples/place_texture.gdshader
+vec4 place_texture(sampler2D sampler, vec2 uv, vec2 texture_pixel_size, vec2 offset, vec2 scale) {
+	vec2 texture_size = vec2(textureSize(sampler, 0));
+	// position of current pixel; sample color c
+	vec2 pos = (uv - offset) / (texture_size*texture_pixel_size) / scale;
+	vec4 c = texture(sampler, pos);
+	// top-left bounds
+	vec2 a = offset;
+	// bottom-right bounds
+	vec2 b = offset + (texture_size*texture_pixel_size) * scale;
+	// check bounds
+	if (
+		a.x  < uv.x && a.y  < uv.y
+		&& b.x > uv.x && b.y > uv.y
+	) { return c; } // within bounds -> return color
+	return vec4(0); // not within bounds -> return transparency
+}