put shell in subdir, and add nix package

shell/shaders/vertexgradient.vert

@@ -0,0 +1,21 @@
+#version 440
+
+layout(location = 0) in vec4 qt_Vertex;
+layout(location = 1) in vec2 qt_MultiTexCoord0;
+
+layout(location = 0) out vec2 coord;
+
+layout(std140, binding = 0) uniform buf {
+    mat4 qt_Matrix;
+    vec4 topLeftColor;
+    vec4 topRightColor;
+    vec4 bottomLeftColor;
+    vec4 bottomRightColor;
+} ubuf;
+
+out gl_PerVertex { vec4 gl_Position; };
+
+void main() {
+    coord = qt_MultiTexCoord0;
+    gl_Position = ubuf.qt_Matrix * qt_Vertex;
+}