1 files changed, 22 insertions, 0 deletions
diff --git a/system/shaders/GL/1.5/gl_stretch.glsl b/system/shaders/GL/1.5/gl_stretch.glsl
new file mode 100644
index 0000000..9a31e54
--- /dev/null
+++ b/system/shaders/GL/1.5/gl_stretch.glsl
@@ -0,0 +1,22 @@
+#version 150
+
+uniform sampler2D img;
+uniform float m_stretch;
+uniform float m_alpha;
+in vec2 m_cord;
+out vec4 fragColor;
+
+vec2 stretch(vec2 pos)
+{
+  // our transform should map [0..1] to itself, with f(0) = 0, f(1) = 1, f(0.5) = 0.5, and f'(0.5) = b.
+  // a simple curve to do this is g(x) = b(x-0.5) + (1-b)2^(n-1)(x-0.5)^n + 0.5
+  // where the power preserves sign. n = 2 is the simplest non-linear case (required when b != 1)
+  float x = pos.x - 0.5;
+  return vec2(mix(x * abs(x) * 2.0, x, m_stretch) + 0.5, pos.y);
+}
+
+void main()
+{
+  fragColor.rgb = texture(img, stretch(m_cord)).rgb;
+  fragColor.a = m_alpha;
+}