From 41e3f9505d63178b40cbc934c03474b1701e7bf9 Mon Sep 17 00:00:00 2001
From: Rein van der Woerd <reinvanderwoerd@me.com>
Date: Sun, 16 Feb 2020 11:00:40 +0100
Subject: [PATCH 1/2] Added Matt DesLauriers' crosshatch shader as a Filter...

It's also using Hugh Kennedy's glsl-luma, which is a dependency of glsl-crosshatch-filter.
---
 orx-fx/src/main/kotlin/dither/Crosshatch.kt   | 30 ++++++++++
 .../extra/fx/gl3/dither/crosshatch.frag       | 55 +++++++++++++++++++
 2 files changed, 85 insertions(+)
 create mode 100644 orx-fx/src/main/kotlin/dither/Crosshatch.kt
 create mode 100644 orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/dither/crosshatch.frag

diff --git a/orx-fx/src/main/kotlin/dither/Crosshatch.kt b/orx-fx/src/main/kotlin/dither/Crosshatch.kt
new file mode 100644
index 00000000..b4006e2d
--- /dev/null
+++ b/orx-fx/src/main/kotlin/dither/Crosshatch.kt
@@ -0,0 +1,30 @@
+package org.openrndr.extra.fx.dither
+
+import org.openrndr.draw.Filter
+import org.openrndr.draw.Shader
+import org.openrndr.extra.fx.filterFragmentCode
+import org.openrndr.extra.parameters.Description
+import org.openrndr.extra.parameters.DoubleParameter
+
+
+@Description("Crosshatch")
+class Crosshatch: Filter(Shader.createFromCode(filterVertexCode, filterFragmentCode("dither/crosshatch.frag"))) {
+    @DoubleParameter("threshold 1", 0.0, 1.0)
+    var t1: Double by parameters
+
+    @DoubleParameter("threshold 2", 0.0, 1.0)
+    var t2: Double by parameters
+
+    @DoubleParameter("threshold 3", 0.0, 1.0)
+    var t3: Double by parameters
+
+    @DoubleParameter("threshold 4", 0.0, 1.0)
+    var t4: Double by parameters
+
+    init {
+        t1 = 1.0
+        t2 = 0.75
+        t3 = 0.5
+        t4 = 0.3
+    }
+}
\ No newline at end of file
diff --git a/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/dither/crosshatch.frag b/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/dither/crosshatch.frag
new file mode 100644
index 00000000..8397a225
--- /dev/null
+++ b/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/dither/crosshatch.frag
@@ -0,0 +1,55 @@
+#version 330
+
+in vec2 v_texCoord0;
+uniform sampler2D tex0;
+out vec4 o_color;
+
+// thresholds
+uniform float t1;
+uniform float t2;
+uniform float t3;
+uniform float t4;
+
+
+// glsl-luma
+float luma(vec3 color) {
+    return dot(color, vec3(0.299, 0.587, 0.114));
+}
+
+float luma(vec4 color) {
+    return dot(color.rgb, vec3(0.299, 0.587, 0.114));
+}
+
+// glsl-crosshatch
+vec3 crosshatch(vec3 texColor, float t1, float t2, float t3, float t4) {
+    float lum = luma(texColor);
+    vec3 color = vec3(1.0);
+    if (lum < t1) {
+        if (mod(gl_FragCoord.x + gl_FragCoord.y, 10.0) == 0.0) {
+            color = vec3(0.0);
+        }
+    }
+    if (lum < t2) {
+        if (mod(gl_FragCoord.x - gl_FragCoord.y, 10.0) == 0.0) {
+            color = vec3(0.0);
+        }
+    }
+    if (lum < t3) {
+        if (mod(gl_FragCoord.x + gl_FragCoord.y - 5.0, 10.0) == 0.0) {
+            color = vec3(0.0);
+        }
+    }
+    if (lum < t4) {
+        if (mod(gl_FragCoord.x - gl_FragCoord.y - 5.0, 10.0) == 0.0) {
+            color = vec3(0.0);
+        }
+    }
+    return color;
+}
+
+
+void main() {
+    vec4 color = texture(tex0, v_texCoord0);
+    o_color.rgb = crosshatch(color.rgb, t1, t2, t3, t4);
+    o_color.a = color.a;
+}
\ No newline at end of file

From 361431d903e9aa8ceb6a9bff0e313d577071b88f Mon Sep 17 00:00:00 2001
From: Edwin Jakobs <edwin@rndr.studio>
Date: Sun, 16 Feb 2020 17:46:39 +0100
Subject: [PATCH 2/2] Fix premultiplied alpha in-output of crosshatch shader

---
 .../org/openrndr/extra/fx/gl3/dither/crosshatch.frag          | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/dither/crosshatch.frag b/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/dither/crosshatch.frag
index 8397a225..6b5fc0e5 100644
--- a/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/dither/crosshatch.frag
+++ b/orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/dither/crosshatch.frag
@@ -50,6 +50,6 @@ vec3 crosshatch(vec3 texColor, float t1, float t2, float t3, float t4) {
 
 void main() {
     vec4 color = texture(tex0, v_texCoord0);
-    o_color.rgb = crosshatch(color.rgb, t1, t2, t3, t4);
-    o_color.a = color.a;
+    vec3 demultiplied = color.a == 0.0 ? vec3(0.0) : color.rgb/color.a;
+    o_color = vec4(crosshatch(demultiplied, t1, t2, t3, t4), 1.0) * color.a;
 }
\ No newline at end of file