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diff --git a/hacks/glx/glsl-utils.h b/hacks/glx/glsl-utils.h
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+/* glsl-utils.h --- support functions for GLSL in OpenGL hacks.
+ * Copyright (c) 2020-2021 Carsten Steger <carsten@mirsanmir.org>
+ *
+ * Permission to use, copy, modify, distribute, and sell this software and its
+ * documentation for any purpose is hereby granted without fee, provided that
+ * the above copyright notice appear in all copies and that both that
+ * copyright notice and this permission notice appear in supporting
+ * documentation.  No representations are made about the suitability of this
+ * software for any purpose.  It is provided "as is" without express or 
+ * implied warranty.
+ */
+
+
+#ifndef __GLSL_UTILS_H__
+#define __GLSL_UTILS_H__
+
+#ifdef HAVE_GLSL
+
+
+/* Column-major linearized matrix coordinate */
+#define GLSL__LINCOOR(r,c,h) ((c)*(h)+(r))
+
+
+/* Copy a 4x4 column-major matrix: c = m. */
+extern void glsl_CopyMatrix(GLfloat c[16], GLfloat m[16]);
+
+/* Create a 4x4 column-major identity matrix. */
+extern void glsl_Identity(GLfloat c[16]);
+
+/* Multiply two 4x4 column-major matrices: c = c*m. */
+extern void glsl_MultMatrix(GLfloat c[16], GLfloat m[16]);
+
+/* Multiply a 4x4 column-major matrix by a rotation matrix that rotates
+   around the axis (x,y,z) by the angle angle: c = c*r(angle,x,y,z). */
+extern void glsl_Rotate(GLfloat c[16], GLfloat angle, GLfloat x, GLfloat y,
+                        GLfloat z);
+
+/* Multiply a 4x4 column-major matrix by a matrix that stretches, shrinks,
+   or reflects an object along the axes: c = c*s(sx,sy,sz). */
+extern void glsl_Scale(GLfloat c[16], GLfloat sx, GLfloat sy, GLfloat sz);
+
+/* Multiply a 4x4 column-major matrix by a matrix that translates an object
+   by a translation vector: c = c*t(tx,ty,tz). */
+extern void glsl_Translate(GLfloat c[16], GLfloat tx, GLfloat ty, GLfloat tz);
+
+/* Add a perspective projection to a 4x4 column-major matrix. */
+extern void glsl_Perspective(GLfloat c[16], GLfloat fovy, GLfloat aspect,
+                             GLfloat z_near, GLfloat z_far);
+
+/* Add an orthographic projection to a 4x4 column-major matrix. */
+extern void glsl_Orthographic(GLfloat c[16], GLfloat left, GLfloat right,
+                              GLfloat bottom, GLfloat top,
+                              GLfloat nearval, GLfloat farval);
+
+/* Get the OpenGL and GLSL versions. */
+extern GLboolean glsl_GetGlAndGlslVersions(GLint *gl_major,
+                                           GLint *gl_minor,
+                                           GLint *glsl_major,
+                                           GLint *glsl_minor,
+                                           GLboolean *gl_gles3);
+
+/* Compile and link a vertex and a Fragment shader into a GLSL program. */
+extern GLboolean glsl_CompileAndLinkShaders(GLsizei vertex_shader_count,
+                                        const GLchar **vertex_shader_source,
+                                        GLsizei fragment_shader_count,
+                                        const GLchar **fragment_shader_source,
+                                        GLuint *shader_program);
+
+
+#endif /* HAVE_GLSL */
+
+
+#endif /* __GLSL_UTILS_H__ */