deinterlace_effect.cpp

#include <epoxy/gl.h>

#include "deinterlace_effect.h"
#include "util.h"

using namespace std;

namespace movit {

DeinterlaceEffect::DeinterlaceEffect()
	: enable_spatial_interlacing_check(true),
	  current_field_position(TOP),
	  num_lines(1080)
{
	register_int("enable_spatial_interlacing_check", (int *)&enable_spatial_interlacing_check);
	register_int("current_field_position", (int *)&current_field_position);
	register_uniform_float("num_lines", &num_lines);
	register_uniform_float("inv_width", &inv_width);
	register_uniform_float("self_offset", &self_offset);
	register_uniform_float_array("current_offset", current_offset, 2);
	register_uniform_float_array("other_offset", other_offset, 3);
}

string DeinterlaceEffect::output_fragment_shader()
{
	char buf[256];
	snprintf(buf, sizeof(buf), "#define YADIF_ENABLE_SPATIAL_INTERLACING_CHECK %d\n",
		enable_spatial_interlacing_check);
	string frag_shader = buf;

	frag_shader += read_file("deinterlace_effect.frag");
	return frag_shader;
}

void DeinterlaceEffect::inform_input_size(unsigned input_num, unsigned width, unsigned height)
{
	assert(input_num >= 0 && input_num < 5);
	widths[input_num] = width;
	heights[input_num] = height;
	num_lines = height * 2;
}

void DeinterlaceEffect::get_output_size(unsigned *width, unsigned *height,
                                        unsigned *virtual_width, unsigned *virtual_height) const
{
	assert(widths[0] == widths[1]);
	assert(widths[1] == widths[2]);
	assert(widths[2] == widths[3]);
	assert(widths[3] == widths[4]);
	assert(heights[0] == heights[1]);
	assert(heights[1] == heights[2]);
	assert(heights[2] == heights[3]);
	assert(heights[3] == heights[4]);
	*width = *virtual_width = widths[0];
	*height = *virtual_height = heights[0] * 2;
}

void DeinterlaceEffect::set_gl_state(GLuint glsl_program_num, const string &prefix, unsigned *sampler_num)
{
	Effect::set_gl_state(glsl_program_num, prefix, sampler_num);

	inv_width = 1.0 / widths[0];

	// Texel centers: t = output texel center for top field, b = for bottom field,
	// x = the input texel. (The same area is two pixels for output, one for input;
	// thus the stippled line in the middle.)
	//
	// +---------+
	// |         |
	// |    t    |
	// |         |
	// | - -x- - |
	// |         |
	// |    b    |
	// |         |
	// +---------+
	//
	// Note as usual OpenGL's bottom-left convention.
	if (current_field_position == 0) {
		// Top.
		self_offset = -0.5 / num_lines;
	} else {
		// Bottom.
		assert(current_field_position == 1);
		self_offset = 0.5 / num_lines;
	}

	// Having now established where the texels lie for the uninterpolated samples,
	// we can use that to figure out where to sample for the interpolation. Drawing
	// the fields as what lines they represent, here for three-pixel high fields
	// with current_field_position == 0 (plus an “o” to mark the pixel we're trying
	// to interpolate, and “c” for corresponding texel in the other field):
	//
	// Prev Cur Next
	//       x
	//   x       x
	//       x
	//   c   o   c
	//       x
	//   x       x
	//
	// Obviously, for sampling in the current field, we are one half-texel off
	// compared to <self_offset>, so sampling in the current field is easy:
	current_offset[0] = self_offset - 0.5 / heights[0];
	current_offset[1] = self_offset + 0.5 / heights[0];

	// Now to find the texel in the other fields corresponding to the pixel
	// we're trying to interpolate, let's realign the diagram above:
	//
	// Prev Cur Next
	//   x   x   x
	//
	//   c   x   c
	//       o
	//   x   x   x
	//
	// So obviously for this case, we need to center on the same place as
	// current_offset[1] (the texel directly above the o; note again the
	// bottom-left convention). For the case of current_field_position == 1,
	// the shift in the alignment goes the other way, and what we want
	// is current_offset[0] (the texel directly below the o).
	float center_offset = current_offset[1 - current_field_position];
	other_offset[0] = center_offset - 1.0 / heights[0];
	other_offset[1] = center_offset;
	other_offset[2] = center_offset + 1.0 / heights[0];
}

}  // namespace movit