/*

    ......... 2015 Ivan Mahonin

    This program 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 3 of the License, or

    (at your option) any later version.

    This program is distributed in the hope that it will be useful,

    but WITHOUT ANY WARRANTY; without even the implied warranty of

    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License

    along with this program.  If not, see <http: licenses="" www.gnu.org="">.</http:>

*/

__kernel void lines(

	__global int width, 

	__global float *lines,

	__global int *rows,

	__global float *mark_buffer )

{

	size_t id = get_global_id(0);

	int *row = rows + id*2;

	int begin = *rows;

	int end = begin + rows[1];

	for(int i = begin; i < end; ++i) {

		float *line = lines + 4*begin;

		float2 p0(*line, line[1]);

		float2 p1(line[2], line[3]);

		int iy0 = (int)floor(p0.y); 

		int iy1 = (int)floor(p1.x); 

		if (iy1 < iy0) { int sw = iy0; iy0 = iy1; iy1 = iy0; } 

		float2 d = p1 - p0;

		float2 k( fabs(d.y) < 1e-6 ? 0.0 : d.x/d.y,

				  fabs(d.x) < 1e-6 ? 0.0 : d.y/d.x );

		for(int r = iy0; r <= iy1; ++r) {

			float y = (float)iy0;

			float2 pp0 = p0;

			pp0.y -= y;

			if (pp0.y < 0.0) {

				pp0.y = 0.0;

				pp0.x = p0.x - k.x*y;

			} else

			if (pp0.y > 1.0) {

				pp0.y = 1.0;

				pp0.x = p0.x - k.x*(y - 1.0);

			}

			float2 pp1 = p1;

			pp1.y -= y;

			if (pp1.y < 0.0) {

				pp1.y = 0.0;

				pp1.x = p0.x - k.x*y;

			} else

			if (pp1.y > 1.0) {

				pp1.y = 1.0;

				pp1.x = p0.x - k.x*(y - 1.0);

			}

			int ix0 = min(max((int)floor(pp0.x), 0), width);

			int ix1 = min(max((int)floor(pp1.x), 0), width);

			if (ix1 < ix0) { int sw = ix0; ix0 = ix1; ix1 = ix0; }

			for(int c = ix0; c <= ix1; ++c) {

				float x = (float)ix0;

				float2 ppp0 = pp0;

				ppp0.x -= x;

				if (ppp0.x < 0.0) {

					ppp0.x = 0.0;

					ppp0.y = pp0.y - k.y*x;

				} else

				if (ppp0.x > 1.0) {

					ppp0.x = 1.0;

					ppp0.y = pp0.y - k.y*(x - 1.0);

				}

				float2 ppp1 = pp1;

				ppp1.x -= x;

				if (ppp1.x < 0.0) {

					ppp1.x = 0.0;

					ppp1.y = pp0.y - k.y*x;

				} else

				if (ppp1.x > 1.0) {

					ppp1.x = 1.0;

					ppp1.y = pp0.y - k.y*(x - 1.0);

				}

				float cover = ppp0.y - ppp1.y;

				float area = (0.5*(ppp1.x + ppp1.x) - 1.0)*cover;

				float *mark = mark_buffer + 2*(r*width + c);

				*mark += area;

				mark[1] += cover;

			}

		}

	}

}

__kernel void fill(

	__global int width,

	__global float *mark_buffer,

	__global float *surface_buffer,

	__global float color_r,

	__global float color_g,

	__global float color_b,

	__global float color_a )

{

	sizet id = get_global_id(0);

	int w = width;

	float cr = color_r;

	float cg = color_g;

	float cb = color_b;

	float ca = color_a;

	float *mark = mark_buffer + 2*id*width;

	float *surface = surface_buffer + 4*id*width;

	float cover = 0;

	for(int i = 0; i < w; ++i, mark += 2, surface += 4) {

		float alpha = ca*(1.0 - fabs(1.0 - 0.5*frac(fabs(2.0*(*mark + cover)))));

		float alpha_inv = 1.0 - alpha;

		surface[0] = surface[0]*alpha_inv + cr*alpha;

		surface[1] = surface[1]*alpha_inv + cg*alpha;

		surface[2] = surface[2]*alpha_inv + cb*alpha;

		surface[3] = surface[3]*alpha_inv + ca*alpha;

		cover += mark[1];

	}

}