scummvm/graphics/tinygl/clip.cpp

/* ScummVM - Graphic Adventure Engine
 *
 * ScummVM is the legal property of its developers, whose names
 * are too numerous to list here. Please refer to the COPYRIGHT
 * file distributed with this source distribution.
 *
 * 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://www.gnu.org/licenses/>.
 *
 */

/*
 * This file is based on, or a modified version of code from TinyGL (C) 1997-2022 Fabrice Bellard,
 * which is licensed under the MIT license (see LICENSE).
 * It also has modifications by the ResidualVM-team, which are covered under the GPLv2 (or later).
 */

#include "graphics/tinygl/zgl.h"

namespace TinyGL {

// fill triangle profile
// #define TINYGL_PROFILE

#define CLIP_XMIN   (1 << 0)
#define CLIP_XMAX   (1 << 1)
#define CLIP_YMIN   (1 << 2)
#define CLIP_YMAX   (1 << 3)
#define CLIP_ZMIN   (1 << 4)
#define CLIP_ZMAX   (1 << 5)

void GLContext::gl_transform_to_viewport(GLVertex *v) {
	float winv;

	// coordinates
	winv = (float)(1.0 / v->pc.W);
	v->zp.x = (int)(v->pc.X * winv * viewport.scale.X + viewport.trans.X);
	v->zp.y = (int)(v->pc.Y * winv * viewport.scale.Y + viewport.trans.Y);
	v->zp.z = (int)(v->pc.Z * winv * viewport.scale.Z + viewport.trans.Z);
	// color
	v->zp.r = (int)(v->color.X * ZB_POINT_RED_MAX);
	v->zp.g = (int)(v->color.Y * ZB_POINT_GREEN_MAX);
	v->zp.b = (int)(v->color.Z * ZB_POINT_BLUE_MAX);
	v->zp.a = (int)(v->color.W * ZB_POINT_ALPHA_MAX);

	// texture
	if (texture_2d_enabled) {
		v->zp.s = (int)(v->tex_coord.X * ZB_POINT_ST_MAX);
		v->zp.t = (int)(v->tex_coord.Y * ZB_POINT_ST_MAX);
	}
}

void GLContext::gl_add_select1(int z1, int z2, int z3) {
	int min, max;

	min = max = z1;
	if (z2 < min)
		min = z2;
	if (z3 < min)
		min = z3;
	if (z2 > max)
		max = z2;
	if (z3 > max)
		max = z3;

	gl_add_select(0xffffffff - min, 0xffffffff - max);
}

// point

void GLContext::gl_draw_point(GLVertex *p0) {
	if (p0->clip_code == 0) {
		if (render_mode == TGL_SELECT) {
			gl_add_select(p0->zp.z, p0->zp.z);
		} else {
			fb->plot(&p0->zp);
		}
	}
}

// line

static inline void interpolate_color(GLContext *c, GLVertex *q, GLVertex *p0, GLVertex *p1, float t) {
	if (c->current_shade_model == TGL_SMOOTH)
		q->color = p0->color + (p1->color - p0->color) * t;
	else
		q->color = p0->color;
}

static inline void interpolate(GLContext *c, GLVertex *q, GLVertex *p0, GLVertex *p1, float t) {
	q->pc = p0->pc + (p1->pc - p0->pc) * t;
	interpolate_color(c, q, p0, p1, t);
}

// Line Clipping

// Line Clipping algorithm from 'Computer Graphics', Principles and
// Practice
static inline int ClipLine1(float denom, float num, float *tmin, float *tmax) {
	float t;

	if (denom > 0) {
		t = num / denom;
		if (t > *tmax)
			return 0;
		if (t > *tmin)
			*tmin = t;
	} else if (denom < 0) {
		t = num / denom;
		if (t < *tmin)
			return 0;
		if (t < *tmax)
			*tmax = t;
	} else if (num > 0)
		return 0;

	return 1;
}

void GLContext::gl_draw_line(GLVertex *p1, GLVertex *p2) {
	float dx, dy, dz, dw, x1, y1, z1, w1;
	float tmin, tmax;
	GLVertex q1, q2;
	int cc1, cc2;

	cc1 = p1->clip_code;
	cc2 = p2->clip_code;

	if ((cc1 | cc2) == 0) {
		if (render_mode == TGL_SELECT) {
			gl_add_select1(p1->zp.z, p2->zp.z, p2->zp.z);
		} else {
			if (depth_test_enabled)
				fb->fillLineZ(&p1->zp, &p2->zp);
			else
				fb->fillLine(&p1->zp, &p2->zp);
		}
	} else if ((cc1 & cc2) != 0) {
		return;
	} else {
		dx = p2->pc.X - p1->pc.X;
		dy = p2->pc.Y - p1->pc.Y;
		dz = p2->pc.Z - p1->pc.Z;
		dw = p2->pc.W - p1->pc.W;
		x1 = p1->pc.X;
		y1 = p1->pc.Y;
		z1 = p1->pc.Z;
		w1 = p1->pc.W;

		tmin = 0;
		tmax = 1;
		if (ClipLine1(dx + dw, -x1 - w1, &tmin, &tmax) &&
				ClipLine1(-dx + dw, x1 - w1, &tmin, &tmax) &&
				ClipLine1(dy + dw, -y1 - w1, &tmin, &tmax) &&
				ClipLine1(-dy + dw, y1 - w1, &tmin, &tmax) &&
				ClipLine1(dz + dw, -z1 - w1, &tmin, &tmax) &&
				ClipLine1(-dz + dw, z1 - w1, &tmin, &tmax)) {
			interpolate(this, &q1, p1, p2, tmin);
			interpolate(this, &q2, p1, p2, tmax);
			gl_transform_to_viewport(&q1);
			gl_transform_to_viewport(&q2);

			if (depth_test_enabled)
				fb->fillLineZ(&q1.zp, &q2.zp);
			else
				fb->fillLine(&q1.zp, &q2.zp);
		}
	}
}

// triangle

// Clipping

// We clip the segment [a,b] against the 6 planes of the normal volume.
// We compute the point 'c' of intersection and the value of the parameter 't'
// of the intersection if x=a+t(b-a).

#define clip_func(name, sign, dir, dir1, dir2) \
static float name(Vector4 *c, Vector4 *a, Vector4 *b) { \
	float t, dX, dY, dZ, dW, den;\
	dX = (b->X - a->X); \
	dY = (b->Y - a->Y); \
	dZ = (b->Z - a->Z); \
	dW = (b->W - a->W); \
	den = -(sign d ## dir) + dW; \
	if (den == 0) \
		t = 0; \
	else \
		t = (sign a->dir - a->W) / den; \
	c-> dir1 = (a->dir1 + t * d ## dir1); \
	c-> dir2 = (a->dir2 + t * d ## dir2); \
	c->W = (a->W + t * dW); \
	c-> dir = (sign c->W); \
	return t; \
}

clip_func(clip_xmin, -, X, Y, Z)
clip_func(clip_xmax, +, X, Y, Z)
clip_func(clip_ymin, -, Y, X, Z)
clip_func(clip_ymax, +, Y, X, Z)
clip_func(clip_zmin, -, Z, X, Y)
clip_func(clip_zmax, +, Z, X, Y)

float(*clip_proc[6])(Vector4 *, Vector4 *, Vector4 *) =  {
	clip_xmin, clip_xmax,
	clip_ymin, clip_ymax,
	clip_zmin, clip_zmax
};

static inline void updateTmp(GLContext *c, GLVertex *q, GLVertex *p0, GLVertex *p1, float t) {
	interpolate_color(c, q, p0, p1, t);

	if (c->texture_2d_enabled) {
		// NOTE: This could be implemented with operator overloading,
		// but i'm not 100% sure that we can completely disregard Z and W components so I'm leaving it like this for now.
		q->tex_coord.X = (p0->tex_coord.X + (p1->tex_coord.X - p0->tex_coord.X) * t);
		q->tex_coord.Y = (p0->tex_coord.Y + (p1->tex_coord.Y - p0->tex_coord.Y) * t);
	}

	q->clip_code = gl_clipcode(q->pc.X, q->pc.Y, q->pc.Z, q->pc.W);
	if (q->clip_code == 0)
		c->gl_transform_to_viewport(q);
}

void GLContext::gl_draw_triangle(GLVertex *p0, GLVertex *p1, GLVertex *p2) {
	int co, c_and, cc[3], front;
	float norm;

	cc[0] = p0->clip_code;
	cc[1] = p1->clip_code;
	cc[2] = p2->clip_code;

	co = cc[0] | cc[1] | cc[2];

	// we handle the non clipped case here to go faster
	if (co == 0) {
		norm = (float)(p1->zp.x - p0->zp.x) * (float)(p2->zp.y - p0->zp.y) -
			   (float)(p2->zp.x - p0->zp.x) * (float)(p1->zp.y - p0->zp.y);
		if (norm == 0)
			return;

		front = norm < 0.0;
		front = front ^ current_front_face;

		// back face culling
		if (cull_face_enabled) {
			// most used case first */
			if (current_cull_face == TGL_BACK) {
				if (front == 0)
					return;
				draw_triangle_front(this, p0, p1, p2);
			} else if (current_cull_face == TGL_FRONT) {
				if (front != 0)
					return;
				draw_triangle_back(this, p0, p1, p2);
			} else {
				return;
			}
		} else {
			// no culling
			if (front) {
				draw_triangle_front(this, p0, p1, p2);
			} else {
				draw_triangle_back(this, p0, p1, p2);
			}
		}
	} else {
		c_and = cc[0] & cc[1] & cc[2];
		if (c_and == 0) {
			gl_draw_triangle_clip(p0, p1, p2, 0);
		}
	}
}

void GLContext::gl_draw_triangle_clip(GLVertex *p0, GLVertex *p1, GLVertex *p2, int clip_bit) {
	int co, c_and, co1, cc[3], edge_flag_tmp, clip_mask;
	GLVertex tmp1, tmp2, *q[3];
	float tt;

	cc[0] = p0->clip_code;
	cc[1] = p1->clip_code;
	cc[2] = p2->clip_code;

	co = cc[0] | cc[1] | cc[2];
	if (co == 0) {
		gl_draw_triangle(p0, p1, p2);
	} else {
		c_and = cc[0] & cc[1] & cc[2];
		// the triangle is completely outside
		if (c_and != 0)
			return;

		// find the next direction to clip
		while (clip_bit < 6 && (co & (1 << clip_bit)) == 0) {
			clip_bit++;
		}

		// this test can be true only in case of rounding errors
		if (clip_bit == 6) {
#if 0
			printf("Error:\n");
			printf("%f %f %f %f\n", p0->pc.X, p0->pc.Y, p0->pc.Z, p0->pc.W);
			printf("%f %f %f %f\n", p1->pc.X, p1->pc.Y, p1->pc.Z, p1->pc.W);
			printf("%f %f %f %f\n", p2->pc.X, p2->pc.Y, p2->pc.Z, p2->pc.W);
#endif
			return;
		}

		clip_mask = 1 << clip_bit;
		co1 = (cc[0] ^ cc[1] ^ cc[2]) & clip_mask;

		if (co1)  {
			// one point outside
			if (cc[0] & clip_mask) {
				q[0] = p0; q[1] = p1; q[2] = p2;
			} else if (cc[1] & clip_mask) {
				q[0] = p1; q[1] = p2; q[2] = p0;
			} else {
				q[0] = p2; q[1] = p0; q[2] = p1;
			}

			tt = clip_proc[clip_bit](&tmp1.pc, &q[0]->pc, &q[1]->pc);
			updateTmp(this, &tmp1, q[0], q[1], tt);

			tt = clip_proc[clip_bit](&tmp2.pc, &q[0]->pc, &q[2]->pc);
			updateTmp(this, &tmp2, q[0], q[2], tt);

			tmp1.edge_flag = q[0]->edge_flag;
			edge_flag_tmp = q[2]->edge_flag;
			q[2]->edge_flag = 0;
			gl_draw_triangle_clip(&tmp1, q[1], q[2], clip_bit + 1);

			tmp2.edge_flag = 1;
			tmp1.edge_flag = 0;
			q[2]->edge_flag = edge_flag_tmp;
			gl_draw_triangle_clip(&tmp2, &tmp1, q[2], clip_bit + 1);
		} else {
			// two points outside
			if ((cc[0] & clip_mask) == 0) {
				q[0] = p0; q[1] = p1; q[2] = p2;
			} else if ((cc[1] & clip_mask) == 0) {
				q[0] = p1; q[1] = p2; q[2] = p0;
			} else {
				q[0] = p2; q[1] = p0; q[2] = p1;
			}

			tt = clip_proc[clip_bit](&tmp1.pc, &q[0]->pc, &q[1]->pc);
			updateTmp(this, &tmp1, q[0], q[1], tt);

			tt = clip_proc[clip_bit](&tmp2.pc, &q[0]->pc, &q[2]->pc);
			updateTmp(this, &tmp2, q[0], q[2], tt);

			tmp1.edge_flag = 1;
			tmp2.edge_flag = q[2]->edge_flag;
			gl_draw_triangle_clip(q[0], &tmp1, &tmp2, clip_bit + 1);
		}
	}
}

void GLContext::gl_draw_triangle_select(GLContext *c, GLVertex *p0, GLVertex *p1, GLVertex *p2) {
	c->gl_add_select1(p0->zp.z, p1->zp.z, p2->zp.z);
}

#ifdef TINYGL_PROFILE
int count_triangles, count_triangles_textured, count_pixels;
#endif

void GLContext::gl_draw_triangle_fill(GLContext *c, GLVertex *p0, GLVertex *p1, GLVertex *p2) {
#ifdef TINYGL_PROFILE
	{
		int norm;
		assert(p0->zp.x >= 0 && p0->zp.x < c->fb->xsize);
		assert(p0->zp.y >= 0 && p0->zp.y < c->fb->ysize);
		assert(p1->zp.x >= 0 && p1->zp.x < c->fb->xsize);
		assert(p1->zp.y >= 0 && p1->zp.y < c->fb->ysize);
		assert(p2->zp.x >= 0 && p2->zp.x < c->fb->xsize);
		assert(p2->zp.y >= 0 && p2->zp.y < c->fb->ysize);

		norm = (p1->zp.x - p0->zp.x) * (p2->zp.y - p0->zp.y) -
				(p2->zp.x - p0->zp.x) * (p1->zp.y - p0->zp.y);
		count_pixels += abs(norm) / 2;
		count_triangles++;
	}
#endif

	if (!c->color_mask_red && !c->color_mask_green && !c->color_mask_blue && !c->color_mask_alpha) {
		c->fb->fillTriangleDepthOnly(&p0->zp, &p1->zp, &p2->zp);
	} else if (c->texture_2d_enabled && c->current_texture->images[0].pixmap) {
#ifdef TINYGL_PROFILE
		count_triangles_textured++;
#endif
		c->fb->setTexture(c->current_texture->images[0].pixmap, c->texture_wrap_s, c->texture_wrap_t);
		if (c->current_shade_model == TGL_SMOOTH) {
			c->fb->fillTriangleTextureMappingPerspectiveSmooth(&p0->zp, &p1->zp, &p2->zp);
		} else {
			c->fb->fillTriangleTextureMappingPerspectiveFlat(&p0->zp, &p1->zp, &p2->zp);
		}
	} else if (c->current_shade_model == TGL_SMOOTH) {
		c->fb->fillTriangleSmooth(&p0->zp, &p1->zp, &p2->zp);
	} else {
		c->fb->fillTriangleFlat(&p0->zp, &p1->zp, &p2->zp);
	}
}

// Render a clipped triangle in line mode

void GLContext::gl_draw_triangle_line(GLContext *c, GLVertex *p0, GLVertex *p1, GLVertex *p2) {
	if (c->depth_test_enabled) {
		if (p0->edge_flag)
			c->fb->fillLineZ(&p0->zp, &p1->zp);
		if (p1->edge_flag)
			c->fb->fillLineZ(&p1->zp, &p2->zp);
		if (p2->edge_flag)
			c->fb->fillLineZ(&p2->zp, &p0->zp);
	} else {
		if (p0->edge_flag)
			c->fb->fillLine(&p0->zp, &p1->zp);
		if (p1->edge_flag)
			c->fb->fillLine(&p1->zp, &p2->zp);
		if (p2->edge_flag)
			c->fb->fillLine(&p2->zp, &p0->zp);
	}
}

// Render a clipped triangle in point mode
void GLContext::gl_draw_triangle_point(GLContext *c, GLVertex *p0, GLVertex *p1, GLVertex *p2) {
	if (p0->edge_flag)
		c->fb->plot(&p0->zp);
	if (p1->edge_flag)
		c->fb->plot(&p1->zp);
	if (p2->edge_flag)
		c->fb->plot(&p2->zp);
}

} // end of namespace TinyGL