-void combine_two_samples(float w1, float w2, float *offset, float *total_weight);
+//
+// Note that since the GPU might have limited precision in its linear
+// interpolation, the effective weights might be different from the ones you
+// asked for. sum_sq_error, if not NULL, will contain the sum of the
+// (estimated) squared errors of the two weights.
+void combine_two_samples(float w1, float w2, float *offset, float *total_weight, float *sum_sq_error);
+
+// Create a VBO with the given data, and bind it to the vertex attribute
+// with name <attribute_name>. Returns the VBO number.
+GLuint fill_vertex_attribute(GLuint glsl_program_num, const std::string &attribute_name, GLint size, GLenum type, GLsizeiptr data_size, const GLvoid *data);
+
+// Clean up after fill_vertex_attribute().
+void cleanup_vertex_attribute(GLuint glsl_program_num, const std::string &attribute_name, GLuint vbo);
+
+} // namespace movit