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SDL_rect.c
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/*
SDL - Simple DirectMedia Layer
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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
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
This library 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
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
Sam Lantinga
slouken@libsdl.org
*/
#include "SDL_config.h"
#include "SDL_video.h"
#include "SDL_rect_c.h"
SDL_bool
SDL_HasIntersection(const SDL_Rect * A, const SDL_Rect * B)
{
int Amin, Amax, Bmin, Bmax;
/* Horizontal intersection */
Amin = A->x;
Amax = Amin + A->w;
Bmin = B->x;
Bmax = Bmin + B->w;
if (Bmin > Amin)
Amin = Bmin;
if (Bmax < Amax)
Amax = Bmax;
if (Amax <= Amin)
return SDL_FALSE;
/* Vertical intersection */
Amin = A->y;
Amax = Amin + A->h;
Bmin = B->y;
Bmax = Bmin + B->h;
if (Bmin > Amin)
Amin = Bmin;
if (Bmax < Amax)
Amax = Bmax;
if (Amax <= Amin)
return SDL_FALSE;
return SDL_TRUE;
}
SDL_bool
SDL_IntersectRect(const SDL_Rect * A, const SDL_Rect * B, SDL_Rect * result)
{
int Amin, Amax, Bmin, Bmax;
/* Horizontal intersection */
Amin = A->x;
Amax = Amin + A->w;
Bmin = B->x;
Bmax = Bmin + B->w;
if (Bmin > Amin)
Amin = Bmin;
result->x = Amin;
if (Bmax < Amax)
Amax = Bmax;
result->w = Amax - Amin;
/* Vertical intersection */
Amin = A->y;
Amax = Amin + A->h;
Bmin = B->y;
Bmax = Bmin + B->h;
if (Bmin > Amin)
Amin = Bmin;
result->y = Amin;
if (Bmax < Amax)
Amax = Bmax;
result->h = Amax - Amin;
return !SDL_RectEmpty(result);
}
void
SDL_UnionRect(const SDL_Rect * A, const SDL_Rect * B, SDL_Rect * result)
{
int Amin, Amax, Bmin, Bmax;
/* Horizontal union */
Amin = A->x;
Amax = Amin + A->w;
Bmin = B->x;
Bmax = Bmin + B->w;
if (Bmin < Amin)
Amin = Bmin;
result->x = Amin;
if (Bmax > Amax)
Amax = Bmax;
result->w = Amax - Amin;
/* Vertical intersection */
Amin = A->y;
Amax = Amin + A->h;
Bmin = B->y;
Bmax = Bmin + B->h;
if (Bmin < Amin)
Amin = Bmin;
result->y = Amin;
if (Bmax > Amax)
Amax = Bmax;
result->h = Amax - Amin;
}
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SDL_bool
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SDL_IntersectRectAndLine(const SDL_Rect * rect, int *X1, int *Y1, int *X2,
int *Y2)
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{
int x1, y1;
int x2, y2;
int rectx1;
int recty1;
int rectx2;
int recty2;
if (!rect || !X1 || !Y1 || !X2 || !Y2) {
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return SDL_FALSE;
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}
x1 = *X1;
y1 = *Y1;
x2 = *X2;
y2 = *Y2;
rectx1 = rect->x;
recty1 = rect->y;
rectx2 = rect->x + rect->w - 1;
recty2 = rect->y + rect->h - 1;
/* Check to see if entire line is inside rect */
if (x1 >= rectx1 && x1 <= rectx2 && x2 >= rectx1 && x2 <= rectx2 &&
y1 >= recty1 && y1 <= recty2 && y2 >= recty1 && y2 <= recty2) {
return SDL_TRUE;
}
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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 < recty1) || (y1 > recty2 && y2 > recty2)) {
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return SDL_FALSE;
}
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if (y1 == y2) {
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/* Horizontal line, easy to clip */
if (x1 < rectx1) {
*X1 = rectx1;
} else if (x1 > rectx2) {
*X1 = rectx2;
}
if (x2 < rectx1) {
*X2 = rectx1;
} else if (x2 > rectx2) {
*X2 = rectx2;
}
return SDL_TRUE;
}
if (x1 == x2) {
/* Vertical line, easy to clip */
if (y1 < recty1) {
*Y1 = recty1;
} else if (y1 > recty2) {
*Y1 = recty2;
}
if (y2 < recty1) {
*Y2 = recty1;
} else if (y2 > recty2) {
*Y2 = recty2;
}
return SDL_TRUE;
}
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else {
/* The task of clipping a line with finite slope ratios in a fixed-
* precision coordinate space is not as immediately simple as it is
* with coordinates of arbitrary precision. If the ratio of slopes
* between the input line segment and the result line segment is not
* a whole number, you have in fact *moved* the line segment a bit,
* and there can be no avoiding it without more precision
*/
int *x_result_[] = { X1, X2, NULL }, **x_result = x_result_;
int *y_result_[] = { Y1, Y2, NULL }, **y_result = y_result_;
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SDL_bool intersection = SDL_FALSE;
double b, m, left, right, bottom, top;
int xl, xh, yl, yh;
/* solve mx+b line formula */
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m = (double) (y1 - y2) / (double) (x1 - x2);
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b = y2 - m * (double) x2;
/* find some linear intersections */
left = (m * (double) rectx1) + b;
right = (m * (double) rectx2) + b;
top = (recty1 - b) / m;
bottom = (recty2 - b) / m;
/* sort end-points' x and y components individually */
if (x1 < x2) {
xl = x1;
xh = x2;
} else {
xl = x2;
xh = x1;
}
if (y1 < y2) {
yl = y1;
yh = y2;
} else {
yl = y2;
yh = y1;
}
#define RISING(a, b, c) (((a)<=(b))&&((b)<=(c)))
/* check for a point that's entirely inside the rect */
if (RISING(rectx1, x1, rectx2) && RISING(recty1, y1, recty2)) {
x_result++;
y_result++;
intersection = SDL_TRUE;
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} else
/* it was determined earlier that *both* end-points are not contained */
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if (RISING(rectx1, x2, rectx2) && RISING(recty1, y2, recty2)) {
**(x_result++) = x2;
**(y_result++) = y2;
intersection = SDL_TRUE;
}
if (RISING(recty1, left, recty2) && RISING(xl, rectx1, xh)) {
**(x_result++) = rectx1;
**(y_result++) = (int) left;
intersection = SDL_TRUE;
}
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if (*x_result == NULL)
return intersection;
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if (RISING(recty1, right, recty2) && RISING(xl, rectx2, xh)) {
**(x_result++) = rectx2;
**(y_result++) = (int) right;
intersection = SDL_TRUE;
}
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if (*x_result == NULL)
return intersection;
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if (RISING(rectx1, top, rectx2) && RISING(yl, recty1, yh)) {
**(x_result++) = (int) top;
**(y_result++) = recty1;
intersection = SDL_TRUE;
}
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if (*x_result == NULL)
return intersection;
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if (RISING(rectx1, bottom, rectx2) && RISING(yl, recty2, yh)) {
**(x_result++) = (int) bottom;
**(y_result++) = recty2;
intersection = SDL_TRUE;
}
return intersection;
}
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return SDL_FALSE;
}
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void
SDL_AddDirtyRect(SDL_DirtyRectList * list, const SDL_Rect * rect)
{
SDL_DirtyRect *dirty;
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/* FIXME: At what point is this optimization too expensive? */
for (dirty = list->list; dirty; dirty = dirty->next) {
if (SDL_HasIntersection(&dirty->rect, rect)) {
SDL_UnionRect(&dirty->rect, rect, &dirty->rect);
return;
}
}
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if (list->free) {
dirty = list->free;
list->free = dirty->next;
} else {
dirty = (SDL_DirtyRect *) SDL_malloc(sizeof(*dirty));
if (!dirty) {
return;
}
}
dirty->rect = *rect;
dirty->next = list->list;
list->list = dirty;
}
void
SDL_ClearDirtyRects(SDL_DirtyRectList * list)
{
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SDL_DirtyRect *prev, *curr;
/* Skip to the end of the free list */
prev = NULL;
for (curr = list->free; curr; curr = curr->next) {
prev = curr;
}
/* Add the list entries to the end */
if (prev) {
prev->next = list->list;
} else {
list->free = list->list;
}
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list->list = NULL;
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}
void
SDL_FreeDirtyRects(SDL_DirtyRectList * list)
{
while (list->list) {
SDL_DirtyRect *elem = list->list;
list->list = elem->next;
SDL_free(elem);
}
while (list->free) {
SDL_DirtyRect *elem = list->free;
list->free = elem->next;
SDL_free(elem);
}
}
/* vi: set ts=4 sw=4 expandtab: */