[blender.git] / intern / raskter / raskter.c

/*
 * ***** BEGIN GPL LICENSE BLOCK *****
 *
 * 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 2
 * 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, write to the Free Software Foundation,
 * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 *
 * The Original Code is Copyright (C) 2012 Blender Foundation.
 * All rights reserved.
 *
 * The Original Code is: all of this file.
 *
 * Contributor(s): Peter Larabell.
 *
 * ***** END GPL LICENSE BLOCK *****
 */

/** \file raskter.c
 *  \ingroup RASKTER
 */

#include <stdlib.h>
#include "raskter.h"

/* from BLI_utildefines.h */
#define MIN2(x, y)               ( (x) < (y) ? (x) : (y) )
#define MAX2(x, y)               ( (x) > (y) ? (x) : (y) )
#define ABS(a)                   ( (a) < 0 ? (-(a)) : (a) )

struct PolyVert {
        int x;
        int y;
};

struct e_Status {
        int x;
        int ybeg;
        int xshift;
        int xdir;
        int drift;
        int drift_inc;
        int drift_dec;
        int num;
        struct e_Status *e_next;
};

struct r_BufferStats {
        float *buf;
        int sizex;
        int sizey;
        int ymin;
        int ymax;
        int xmin;
        int xmax;
};

struct r_FillContext {
        struct e_Status *all_edges, *possible_edges;
        struct r_BufferStats rb;
};

/*
 * Sort all the edges of the input polygon by Y, then by X, of the "first" vertex encountered.
 * This will ensure we can scan convert the entire poly in one pass.
 *
 * Really the poly should be clipped to the frame buffer's dimensions here for speed of drawing
 * just the poly. Since the DEM code could end up being coupled with this, we'll keep it separate
 * for now.
 */
static void preprocess_all_edges(struct r_FillContext *ctx,
                                 struct PolyVert *verts, int num_verts, struct e_Status *open_edge)
{
        int i;
        int xbeg;
        int ybeg;
        int xend;
        int yend;
        int dx;
        int dy;
        int temp_pos;
        int xdist;
        struct e_Status *e_new;
        struct e_Status *next_edge;
        struct e_Status **next_edge_ref;
        struct PolyVert *v;
        /* set up pointers */
        v = verts;
        ctx->all_edges = NULL;
        /* initialize some boundaries */
        ctx->rb.xmax = v[0].x;
        ctx->rb.xmin = v[0].x;
        ctx->rb.ymax = v[0].y;
        ctx->rb.ymin = v[0].y;
        /* loop all verts */
        for (i = 0; i < num_verts; i++) {
                /* determine beginnings and endings of edges, linking last vertex to first vertex */
                xbeg = v[i].x;
                ybeg = v[i].y;
                /* keep track of our x and y bounds */
                if (xbeg >= ctx->rb.xmax) {
                        ctx->rb.xmax = xbeg;
                }
                else if (xbeg <= ctx->rb.xmin) {
                        ctx->rb.xmin = xbeg;
                }
                if (ybeg >= ctx->rb.ymax) {
                        ctx->rb.ymax= ybeg;
                }
                else if (ybeg <= ctx->rb.ymin) {
                        ctx->rb.ymin=ybeg;
                }
                if (i) {
                        /* we're not at the last vert, so end of the edge is the previous vertex */
                        xend = v[i - 1].x;
                        yend = v[i - 1].y;
                }
                else {
                        /* we're at the first vertex, so the "end" of this edge is the last vertex */
                        xend = v[num_verts - 1].x;
                        yend = v[num_verts - 1].y;
                }
                /* make sure our edges are facing the correct direction */
                if (ybeg > yend) {
                        /* flip the Xs */
                        temp_pos = xbeg;
                        xbeg = xend;
                        xend = temp_pos;
                        /* flip the Ys */
                        temp_pos = ybeg;
                        ybeg = yend;
                        yend = temp_pos;
                }

                /* calculate y delta */
                dy = yend - ybeg;
                /* dont draw horizontal lines directly, they are scanned as part of the edges they connect, so skip em. :) */
                if (dy) {
                        /* create the edge and determine it's slope (for incremental line drawing) */
                        e_new = open_edge++;

                        /* calculate x delta */
                        dx = xend - xbeg;
                        if (dx > 0) {
                                e_new->xdir = 1;
                                xdist = dx;
                        }
                        else {
                                e_new->xdir = -1;
                                xdist = -dx;
                        }

                        e_new->x = xbeg;
                        e_new->ybeg = ybeg;
                        e_new->num = dy;
                        e_new->drift_dec = dy;

                        /* calculate deltas for incremental drawing */
                        if (dx >= 0) {
                                e_new->drift = 0;
                        }
                        else {
                                e_new->drift = -dy + 1;
                        }
                        if (dy >= xdist) {
                                e_new->drift_inc = xdist;
                                e_new->xshift = 0;
                        }
                        else {
                                e_new->drift_inc = xdist % dy;
                                e_new->xshift = (xdist / dy) * e_new->xdir;
                        }
                        next_edge_ref = &ctx->all_edges;
                        /* link in all the edges, in sorted order */
                        for (;;) {
                                next_edge = *next_edge_ref;
                                if (!next_edge || (next_edge->ybeg > ybeg) || ((next_edge->ybeg == ybeg) && (next_edge->x >= xbeg))) {
                                        e_new->e_next = next_edge;
                                        *next_edge_ref = e_new;
                                        break;
                                }
                                next_edge_ref = &next_edge->e_next;
                        }
                }
        }
}

/*
 * This function clips drawing to the frame buffer. That clipping will likely be moved into the preprocessor
 * for speed, but waiting on final design choices for curve-data before eliminating data the DEM code will need
 * if it ends up being coupled with this function.
 */
static int rast_scan_fill(struct r_FillContext *ctx, struct PolyVert *verts, int num_verts, float intensity)
{
        int x_curr;                 /* current pixel position in X */
        int y_curr;                 /* current scan line being drawn */
        int yp;                     /* y-pixel's position in frame buffer */
        int swixd = 0;              /* whether or not edges switched position in X */
        float *cpxl;                /* pixel pointers... */
        float *mpxl;
        float *spxl;
        struct e_Status *e_curr;    /* edge pointers... */
        struct e_Status *e_temp;
        struct e_Status *edgbuf;
        struct e_Status **edgec;


        /*
         * If the number of verts specified to render as a polygon is less than 3,
         * return immediately. Obviously we cant render a poly with sides < 3. The
         * return for this we set to 1, simply so it can be distinguished from the
         * next place we could return, /home/guest/blender-svn/soc-2011-tomato/intern/raskter/raskter.
         * which is a failure to allocate memory.
         */
        if (num_verts < 3) {
                return(1);
        }

        /*
         * Try to allocate an edge buffer in memory. needs to be the size of the edge tracking data
         * multiplied by the number of edges, which is always equal to the number of verts in
         * a 2D polygon. Here we return 0 to indicate a memory allocation failure, as opposed to a 1 for
         * the preceeding error, which was a rasterization request on a 2D poly with less than
         * 3 sides.
         */
        if ((edgbuf = (struct e_Status *)(malloc(sizeof(struct e_Status) * num_verts))) == NULL) {
                return(0);
        }

        /*
         * Do some preprocessing on all edges. This constructs a table structure in memory of all
         * the edge properties and can "flip" some edges so sorting works correctly.
         */
        preprocess_all_edges(ctx, verts, num_verts, edgbuf);

        /* can happen with a zero area mask */
        if (ctx->all_edges == NULL) {
                free(edgbuf);
                return(1);
        }
        /*
         * Set the pointer for tracking the edges currently in processing to NULL to make sure
         * we don't get some crazy value after initialization.
         */
        ctx->possible_edges = NULL;

        /*
         * Loop through all scan lines to be drawn. Since we sorted by Y values during
         * preprocess_all_edges(), we can already exact values for the lowest and
         * highest Y values we could possibly need by induction. The preprocessing sorted
         * out edges by Y position, we can cycle the current edge being processed once
         * it runs out of Y pixels. When we have no more edges, meaning the current edge
         * is NULL after setting the "current" edge to be the previous current edge's
         * "next" edge in the Y sorted edge connection chain, we can stop looping Y values,
         * since we can't possibly have more scan lines if we ran out of edges. :)
         *
         * TODO: This clips Y to the frame buffer, which should be done in the preprocessor, but for now is done here.
         *       Will get changed once DEM code gets in.
         */
        for (y_curr = ctx->all_edges->ybeg; (ctx->all_edges || ctx->possible_edges); y_curr++) {

                /*
                 * Link any edges that start on the current scan line into the list of
                 * edges currently needed to draw at least this, if not several, scan lines.
                 */

                /*
                 * Set the current edge to the beginning of the list of edges to be rasterized
                 * into this scan line.
                 *
                 * We could have lots of edge here, so iterate over all the edges needed. The
                 * preprocess_all_edges() function sorted edges by X within each chunk of Y sorting
                 * so we safely cycle edges to thier own "next" edges in order.
                 *
                 * At each iteration, make sure we still have a non-NULL edge.
                 */
                for (edgec = &ctx->possible_edges; ctx->all_edges && (ctx->all_edges->ybeg == y_curr);) {
                        x_curr = ctx->all_edges->x;                  /* Set current X position. */
                        for (;;) {                                   /* Start looping edges. Will break when edges run out. */
                                e_curr = *edgec;                         /* Set up a current edge pointer. */
                                if (!e_curr || (e_curr->x >= x_curr)) {  /* If we have an no edge, or we need to skip some X-span, */
                                        e_temp = ctx->all_edges->e_next;     /* set a temp "next" edge to test. */
                                        *edgec = ctx->all_edges;             /* Add this edge to the list to be scanned. */
                                        ctx->all_edges->e_next = e_curr;     /* Set up the next edge. */
                                        edgec = &ctx->all_edges->e_next;     /* Set our list to the next edge's location in memory. */
                                        ctx->all_edges = e_temp;             /* Skip the NULL or bad X edge, set pointer to next edge. */
                                        break;                               /* Stop looping edges (since we ran out or hit empty X span. */
                                }
                                else {
                                        edgec = &e_curr->e_next;             /* Set the pointer to the edge list the "next" edge. */
                                }
                        }
                }

                /*
                 * Determine the current scan line's offset in the pixel buffer based on its Y position.
                 * Basically we just multiply the current scan line's Y value by the number of pixels in each line.
                 */
                yp = y_curr * ctx->rb.sizex;
                /*
                 * Set a "scan line pointer" in memory. The location of the buffer plus the row offset.
                 */
                spxl = ctx->rb.buf + (yp);
                /*
                 * Set up the current edge to the first (in X) edge. The edges which could possibly be in this
                 * list were determined in the preceeding edge loop above. They were already sorted in X by the
                 * initial processing function.
                 *
                 * At each iteration, test for a NULL edge. Since we'll keep cycling edge's to their own "next" edge
                 * we will eventually hit a NULL when the list runs out.
                 */
                for (e_curr = ctx->possible_edges; e_curr; e_curr = e_curr->e_next) {
                        /*
                         * Calculate a span of pixels to fill on the current scan line.
                         *
                         * Set the current pixel pointer by adding the X offset to the scan line's start offset.
                         * Cycle the current edge the next edge.
                         * Set the max X value to draw to be one less than the next edge's first pixel. This way we are
                         * sure not to ever get into a situation where we have overdraw. (drawing the same pixel more than
                         * one time because it's on a vertex connecting two edges)
                         *
                         * Then blast through all the pixels in the span, advancing the pointer and setting the color to white.
                         *
                         * TODO: Here we clip to the scan line, this is not efficient, and should be done in the preprocessor,
                         *       but for now it is done here until the DEM code comes in.
                         */

                        /* set up xmin and xmax bounds on this scan line */
                        cpxl = spxl + MAX2(e_curr->x, 0);
                        e_curr = e_curr->e_next;
                        mpxl = spxl + MIN2(e_curr->x, ctx->rb.sizex) - 1;

                        if ((y_curr >= 0) && (y_curr < ctx->rb.sizey)) {
                                /* draw the pixels. */
                                for (; cpxl <= mpxl; *cpxl++ += intensity) {}
                        }
                }

                /*
                 * Loop through all edges of polygon that could be hit by this scan line,
                 * and figure out their x-intersections with the next scan line.
                 *
                 * Either A.) we wont have any more edges to test, or B.) we just add on the
                 * slope delta computed in preprocessing step. Since this draws non-antialiased
                 * polygons, we dont have fractional positions, so we only move in x-direction
                 * when needed to get all the way to the next pixel over...
                 */
                for (edgec = &ctx->possible_edges; (e_curr = *edgec);) {
                        if (!(--(e_curr->num))) {
                                *edgec = e_curr->e_next;
                        }
                        else {
                                e_curr->x += e_curr->xshift;
                                if ((e_curr->drift += e_curr->drift_inc) > 0) {
                                        e_curr->x += e_curr->xdir;
                                        e_curr->drift -= e_curr->drift_dec;
                                }
                                edgec = &e_curr->e_next;
                        }
                }
                /*
                 * It's possible that some edges may have crossed during the last step, so we'll be sure
                 * that we ALWAYS intersect scan lines in order by shuffling if needed to make all edges
                 * sorted by x-intersection coordinate. We'll always scan through at least once to see if
                 * edges crossed, and if so, we set the 'swixd' flag. If 'swixd' gets set on the initial
                 * pass, then we know we need to sort by x, so then cycle through edges again and perform
                 * the sort.-
                 */
                if (ctx->possible_edges) {
                        for (edgec = &ctx->possible_edges; (e_curr = *edgec)->e_next; edgec = &(*edgec)->e_next) {
                                /* if the current edge hits scan line at greater X than the next edge, we need to exchange the edges */
                                if (e_curr->x > e_curr->e_next->x) {
                                        *edgec = e_curr->e_next;
                                        /* exchange the pointers */
                                        e_temp = e_curr->e_next->e_next;
                                        e_curr->e_next->e_next = e_curr;
                                        e_curr->e_next = e_temp;
                                        /* set flag that we had at least one switch */
                                        swixd = 1;
                                }
                        }
                        /* if we did have a switch, look for more (there will more if there was one) */
                        for (;;) {
                                /* reset exchange flag so it's only set if we encounter another one */
                                swixd = 0;
                                for (edgec = &ctx->possible_edges; (e_curr = *edgec)->e_next; edgec = &(*edgec)->e_next) {
                                        /* again, if current edge hits scan line at higher X than next edge, exchange the edges and set flag */
                                        if (e_curr->x > e_curr->e_next->x) {
                                                *edgec = e_curr->e_next;
                                                /* exchange the pointers */
                                                e_temp = e_curr->e_next->e_next;
                                                e_curr->e_next->e_next = e_curr;
                                                e_curr->e_next = e_temp;
                                                /* flip the exchanged flag */
                                                swixd = 1;
                                        }
                                }
                                /* if we had no exchanges, we're done reshuffling the pointers */
                                if (!swixd) {
                                        break;
                                }
                        }
                }
        }

        free(edgbuf);
        return 1;
}

int PLX_raskterize(float(*base_verts)[2], int num_base_verts,
                   float *buf, int buf_x, int buf_y) {
        int i;                                   /* i: Loop counter. */
        struct PolyVert *ply;                   /* ply: Pointer to a list of integer buffer-space vertex coordinates. */
        struct r_FillContext ctx = {0};
        const float buf_x_f = (float)(buf_x);
        const float buf_y_f = (float)(buf_y);
        /*
         * Allocate enough memory for our PolyVert list. It'll be the size of the PolyVert
         * data structure multiplied by the number of base_verts.
         *
         * In the event of a failure to allocate the memory, return 0, so this error can
         * be distinguished as a memory allocation error.
         */
        if ((ply = (struct PolyVert *)(malloc(sizeof(struct PolyVert) * num_base_verts))) == NULL) {
                return(0);
        }

        ctx.rb.buf = buf;                            /* Set the output buffer pointer. */
        ctx.rb.sizex = buf_x;                        /* Set the output buffer size in X. (width) */
        ctx.rb.sizey = buf_y;                        /* Set the output buffer size in Y. (height) */
        /*
         * Loop over all verts passed in to be rasterized. Each vertex's X and Y coordinates are
         * then converted from normalized screen space (0.0 <= POS <= 1.0) to integer coordinates
         * in the buffer-space coordinates passed in inside buf_x and buf_y.
         *
         * It's worth noting that this function ONLY outputs fully white pixels in a mask. Every pixel
         * drawn will be 1.0f in value, there is no anti-aliasing.
         */

        for (i = 0; i < num_base_verts; i++) {                      /* Loop over all base_verts. */
                ply[i].x = (int)((base_verts[i][0] * buf_x_f) + 0.5f);  /* Range expand normalized X to integer buffer-space X. */
                ply[i].y = (int)((base_verts[i][1] * buf_y_f) + 0.5f);  /* Range expand normalized Y to integer buffer-space Y. */
        }

        i = rast_scan_fill(&ctx, ply, num_base_verts,1.0f);  /* Call our rasterizer, passing in the integer coords for each vert. */

        free(ply);                                      /* Free the memory allocated for the integer coordinate table. */
        return(i);                                      /* Return the value returned by the rasterizer. */
}