1 files changed, 38 insertions, 0 deletions
diff --git a/vcl/opengl/shaders/lineFragmentShader.glsl b/vcl/opengl/shaders/lineFragmentShader.glsl
new file mode 100644
index 000000000..c49570be3
--- /dev/null
+++ b/vcl/opengl/shaders/lineFragmentShader.glsl
@@ -0,0 +1,38 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+#version 130
+
+varying float fade_factor; // 0->1 fade factor used for AA
+uniform vec4 color;
+
+uniform float line_width;
+uniform float feather;
+
+void main()
+{
+    float start = (line_width / 2.0) - feather; // where we start to apply alpha
+    float end = (line_width / 2.0) + feather; // where we end to apply alpha
+
+    // Calculate the multiplier so we can transform the 0->1 fade factor
+    // to take feather and line width into account.
+    float multiplied = 1.0 / (1.0 - (start / end));
+
+    float dist = (1.0 - abs(fade_factor)) * multiplied;
+
+    float alpha = clamp(dist, 0.0, 1.0);
+
+    // modify the alpha channel only
+    vec4 result_color = color;
+    result_color.a = result_color.a * alpha;
+
+    gl_FragColor = result_color;
+}
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */