scm-sample.hpp

// Copyright (C) 2011-2012 Robert Kooima
//
// LIBSCM is free software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the Free Software
// Foundation; either version 2 of the License, or (at your option) any later
// version.
//
// This program is distributed in the hope that it will be useful, but WITH-
// OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
// FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
// more details.

#ifndef SCM_SAMPLE_HPP
#define SCM_SAMPLE_HPP

#include <string>

#include <tiffio.h>

//------------------------------------------------------------------------------

class scm_file;

//------------------------------------------------------------------------------

/// An scm_sample samples an SCM TIFF file
///
/// This facility is used primarily to implement collision detection with the
/// sphere. This is slightly inelegant. The mechanism of the SCM renderer is
/// designed for optimal GPU performance. As such, SCM data is never touched
/// by the render thread. Instead, data moves straight from the loader thread
/// decompressors into the VRAM texture cache via asynchronous transfer.
///
/// Unfortunately, collision detection requires that the main CPU thread have
/// knowledge of SCM height data. This object provides that knowledge. Sadly,
/// data access incurs latency, and the main thread is also the render thread,
/// so collision detection has the potential to delay the generation of the
/// frame, running contrary to the spirit of the entire library.
///
/// It's a necessary evil.

class scm_sample
{
public:

    scm_sample(scm_file *);
   ~scm_sample();

    float get(const double *);

private:

    float lookup(int, int) const;

    TIFF     *tiff;
    scm_file *file;

    double  last_v[3];  // Sample cache last vector
    float   last_k;     // Sample cache last value
    uint64  last_o;     // Sample cache last page offset
    tsize_t last_i0;    // Sample cache last strip
    tsize_t last_i1;    // Sample cache last strip
    uint8  *last_p;     // Sample cache last page buffer
};

//------------------------------------------------------------------------------

#endif