src/video/SDL_rect.c
author Sam Lantinga <slouken@libsdl.org>
Sun, 04 Jan 2009 19:33:21 +0000
changeset 2994 7563b99e9a49
parent 2920 cdb01906cb7e
child 2997 e4f025078c1c
permissions -rw-r--r--
Date: Sat, 3 Jan 2009 22:11:18 -0500 From: "Donny Viszneki" Subject: Re: [SDL] Want to help with SDL 1.3? >> > For example, here's a good quick project for someone from the TODO list: >> > * Add diagonal line clipping to SDL_IntersectRectAndLine() Just wanted to point out that the patch is available at http://codebad.com/rect-line-ix.patch I hereby grant Sam Lantinga an irrevocable non-exclusive distribution license to this patch to do with as he wishes.
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/*
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    SDL - Simple DirectMedia Layer
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99210400e8b9 Updated copyright date
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    Copyright (C) 1997-2009 Sam Lantinga
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    This library is free software; you can redistribute it and/or
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    modify it under the terms of the GNU Lesser General Public
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    License as published by the Free Software Foundation; either
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    version 2.1 of the License, or (at your option) any later version.
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    This library is distributed in the hope that it will be useful,
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    but WITHOUT ANY WARRANTY; without even the implied warranty of
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    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
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    Lesser General Public License for more details.
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    You should have received a copy of the GNU Lesser General Public
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    License along with this library; if not, write to the Free Software
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    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
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    Sam Lantinga
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    slouken@libsdl.org
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*/
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#include "SDL_config.h"
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#include "SDL_video.h"
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#include "SDL_rect_c.h"
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SDL_bool
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SDL_HasIntersection(const SDL_Rect * A, const SDL_Rect * B)
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{
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    int Amin, Amax, Bmin, Bmax;
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    /* Horizontal intersection */
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    Amin = A->x;
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    Amax = Amin + A->w;
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    Bmin = B->x;
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    Bmax = Bmin + B->w;
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    if (Bmin > Amin)
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        Amin = Bmin;
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    if (Bmax < Amax)
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        Amax = Bmax;
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    if (Amax <= Amin)
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        return SDL_FALSE;
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    /* Vertical intersection */
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    Amin = A->y;
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    Amax = Amin + A->h;
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    Bmin = B->y;
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    Bmax = Bmin + B->h;
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    if (Bmin > Amin)
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        Amin = Bmin;
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    if (Bmax < Amax)
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        Amax = Bmax;
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    if (Amax <= Amin)
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        return SDL_FALSE;
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    return SDL_TRUE;
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}
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SDL_bool
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SDL_IntersectRect(const SDL_Rect * A, const SDL_Rect * B, SDL_Rect * result)
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{
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    int Amin, Amax, Bmin, Bmax;
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    /* Horizontal intersection */
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    Amin = A->x;
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    Amax = Amin + A->w;
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    Bmin = B->x;
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    Bmax = Bmin + B->w;
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    if (Bmin > Amin)
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        Amin = Bmin;
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    result->x = Amin;
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    if (Bmax < Amax)
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        Amax = Bmax;
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    result->w = Amax - Amin;
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    /* Vertical intersection */
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    Amin = A->y;
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    Amax = Amin + A->h;
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    Bmin = B->y;
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    Bmax = Bmin + B->h;
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    if (Bmin > Amin)
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        Amin = Bmin;
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    result->y = Amin;
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    if (Bmax < Amax)
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        Amax = Bmax;
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    result->h = Amax - Amin;
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    return !SDL_RectEmpty(result);
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}
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void
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SDL_UnionRect(const SDL_Rect * A, const SDL_Rect * B, SDL_Rect * result)
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{
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    int Amin, Amax, Bmin, Bmax;
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    /* Horizontal union */
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    Amin = A->x;
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    Amax = Amin + A->w;
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    Bmin = B->x;
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    Bmax = Bmin + B->w;
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    if (Bmin < Amin)
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        Amin = Bmin;
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    result->x = Amin;
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    if (Bmax > Amax)
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        Amax = Bmax;
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    result->w = Amax - Amin;
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    /* Vertical intersection */
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    Amin = A->y;
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    Amax = Amin + A->h;
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    Bmin = B->y;
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    Bmax = Bmin + B->h;
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    if (Bmin < Amin)
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        Amin = Bmin;
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    result->y = Amin;
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    if (Bmax > Amax)
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        Amax = Bmax;
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    result->h = Amax - Amin;
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}
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SDL_bool
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SDL_IntersectRectAndLine(const SDL_Rect * rect, int *X1, int *Y1, int *X2,
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                         int *Y2)
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{
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    int x1, y1;
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    int x2, y2;
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    int rectx1;
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    int recty1;
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    int rectx2;
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    int recty2;
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    if (!rect || !X1 || !Y1 || !X2 || !Y2) {
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        SDL_FALSE;
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    }
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    x1 = *X1;
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    y1 = *Y1;
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    x2 = *X2;
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    y2 = *Y2;
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    rectx1 = rect->x;
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    recty1 = rect->y;
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    rectx2 = rect->x + rect->w - 1;
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    recty2 = rect->y + rect->h - 1;
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    /* Check to see if entire line is inside rect */
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    if (x1 >= rectx1 && x1 <= rectx2 && x2 >= rectx1 && x2 <= rectx2 &&
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        y1 >= recty1 && y1 <= recty2 && y2 >= recty1 && y2 <= recty2) {
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        return SDL_TRUE;
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    }
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    /* Check to see if entire line is to one side of rect */
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    if ((x1 < rectx1 && x2 < rectx1) || (x1 > rectx2 && x2 > rectx2) ||
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        (y1 < recty1 && y2 < recty2) || (y1 > recty2 && y2 > recty2)) {
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        return SDL_FALSE;
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    }
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    if (y1 == y2) {
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        /* Horizontal line, easy to clip */
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        if (x1 < rectx1) {
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            *X1 = rectx1;
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        } else if (x1 > rectx2) {
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            *X1 = rectx2;
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        }
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        if (x2 < rectx1) {
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            *X2 = rectx1;
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        } else if (x2 > rectx2) {
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            *X2 = rectx2;
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        }
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        return SDL_TRUE;
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    }
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   171
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    if (x1 == x2) {
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        /* Vertical line, easy to clip */
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        if (y1 < recty1) {
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            *Y1 = recty1;
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   176
        } else if (y1 > recty2) {
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            *Y1 = recty2;
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        }
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        if (y2 < recty1) {
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            *Y2 = recty1;
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   181
        } else if (y2 > recty2) {
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            *Y2 = recty2;
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   183
        }
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        return SDL_TRUE;
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   185
    }
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   186
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    else
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   188
    {
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    /* The task of clipping a line with finite slope ratios in a fixed-
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     * precision coordinate space is not as immediately simple as it is
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     * with coordinates of arbitrary precision. If the ratio of slopes
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     * between the input line segment and the result line segment is not
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     * a whole number, you have in fact *moved* the line segment a bit,
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     * and there can be no avoiding it without more precision
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   195
     */
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        int *x_result_[] = {X1, X2, NULL}, **x_result = x_result_;
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        int *y_result_[] = {Y1, Y2, NULL}, **y_result = y_result_;
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        SDL_bool intersection = SDL_FALSE;
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   199
        double b, m, left, right, bottom, top;
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        int xl, xh, yl, yh;
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   201
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   202
        /* solve mx+b line formula */
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   203
        m = (double)(y1-y2) / (double)(x1-x2);
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   204
        b = y2 - m * (double) x2;
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diff changeset
   205
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   206
        /* find some linear intersections */
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   207
        left = (m * (double) rectx1) + b;
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   208
        right = (m * (double) rectx2) + b;
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   209
        top = (recty1 - b) / m;
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   210
        bottom = (recty2 - b) / m;
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diff changeset
   211
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   212
        /* sort end-points' x and y components individually */
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   213
        if (x1 < x2) {
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   214
            xl = x1;
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   215
            xh = x2;
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diff changeset
   216
        } else {
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   217
            xl = x2;
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   218
            xh = x1;
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diff changeset
   219
        }
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   220
        if (y1 < y2) {
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diff changeset
   221
            yl = y1;
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   222
            yh = y2;
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diff changeset
   223
        } else {
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diff changeset
   224
            yl = y2;
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   225
            yh = y1;
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diff changeset
   226
        }
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diff changeset
   227
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   228
#define RISING(a, b, c) (((a)<=(b))&&((b)<=(c)))
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   229
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   230
        /* check for a point that's entirely inside the rect */
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diff changeset
   231
        if (RISING(rectx1, x1, rectx2) && RISING(recty1, y1, recty2)) {
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diff changeset
   232
            x_result++;
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diff changeset
   233
            y_result++;
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diff changeset
   234
            intersection = SDL_TRUE;
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diff changeset
   235
        } else /* it was determined earlier that *both* end-points are not contained */
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diff changeset
   236
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diff changeset
   237
        if (RISING(rectx1, x2, rectx2) && RISING(recty1, y2, recty2)) {
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diff changeset
   238
            **(x_result++) = x2;
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diff changeset
   239
            **(y_result++) = y2;
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diff changeset
   240
            intersection = SDL_TRUE;
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diff changeset
   241
        }
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diff changeset
   242
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diff changeset
   243
        if (RISING(recty1, left, recty2) && RISING(xl, rectx1, xh)) {
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diff changeset
   244
            **(x_result++) = rectx1;
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diff changeset
   245
            **(y_result++) = (int) left;
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diff changeset
   246
            intersection = SDL_TRUE;
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diff changeset
   247
        }
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diff changeset
   248
7563b99e9a49 Date: Sat, 3 Jan 2009 22:11:18 -0500
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diff changeset
   249
        if (*x_result == NULL) return intersection;
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diff changeset
   250
        if (RISING(recty1, right, recty2) && RISING(xl, rectx2, xh)) {
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diff changeset
   251
            **(x_result++) = rectx2;
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diff changeset
   252
            **(y_result++) = (int) right;
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            intersection = SDL_TRUE;
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        }
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   255
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        if (*x_result == NULL) return intersection;
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        if (RISING(rectx1, top, rectx2) && RISING(yl, recty1, yh)) {
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            **(x_result++) = (int) top;
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            **(y_result++) = recty1;
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            intersection = SDL_TRUE;
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        }
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   262
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        if (*x_result == NULL) return intersection;
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        if (RISING(rectx1, bottom, rectx2) && RISING(yl, recty2, yh)) {
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            **(x_result++) = (int) bottom;
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            **(y_result++) = recty2;
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            intersection = SDL_TRUE;
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        }
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        return intersection;
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    }
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    return SDL_FALSE;
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}
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void
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SDL_AddDirtyRect(SDL_DirtyRectList * list, const SDL_Rect * rect)
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{
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    SDL_DirtyRect *dirty;
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    /* FIXME: At what point is this optimization too expensive? */
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    for (dirty = list->list; dirty; dirty = dirty->next) {
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        if (SDL_HasIntersection(&dirty->rect, rect)) {
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            SDL_UnionRect(&dirty->rect, rect, &dirty->rect);
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            return;
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        }
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    }
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    if (list->free) {
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        dirty = list->free;
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        list->free = dirty->next;
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    } else {
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        dirty = (SDL_DirtyRect *) SDL_malloc(sizeof(*dirty));
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        if (!dirty) {
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            return;
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        }
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    }
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    dirty->rect = *rect;
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    dirty->next = list->list;
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    list->list = dirty;
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}
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void
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SDL_ClearDirtyRects(SDL_DirtyRectList * list)
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{
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    SDL_DirtyRect *prev, *curr;
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    /* Skip to the end of the free list */
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    prev = NULL;
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    for (curr = list->free; curr; curr = curr->next) {
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        prev = curr;
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    }
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    /* Add the list entries to the end */
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    if (prev) {
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        prev->next = list->list;
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    } else {
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        list->free = list->list;
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   319
    }
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    list->list = NULL;
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}
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void
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SDL_FreeDirtyRects(SDL_DirtyRectList * list)
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{
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   326
    while (list->list) {
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        SDL_DirtyRect *elem = list->list;
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        list->list = elem->next;
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   329
        SDL_free(elem);
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   330
    }
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   331
    while (list->free) {
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   332
        SDL_DirtyRect *elem = list->free;
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   333
        list->free = elem->next;
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   334
        SDL_free(elem);
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   335
    }
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   336
}
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/* vi: set ts=4 sw=4 expandtab: */