void inform_input_size(unsigned input_num, unsigned width, unsigned height) override;
void set_gl_state(GLuint glsl_program_num, const std::string &prefix, unsigned *sampler_num) override;
void inform_input_size(unsigned input_num, unsigned width, unsigned height) override;
void set_gl_state(GLuint glsl_program_num, const std::string &prefix, unsigned *sampler_num) override;