Added line clipping

--HG--
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/trunk%403371

src/video/SDL_rect.c

@@ -118,6 +118,75 @@ SDL_UnionRect(const SDL_Rect * A, const SDL_Rect * B, SDL_Rect * result)
     result->h = Amax - Amin;
 }
 
+SDL_bool
+SDL_IntersectRectAndLine(const SDL_Rect *rect, int *X1, int *Y1, int *X2, int *Y2)
+{
+    int x1, y1;
+    int x2, y2;
+    int rectx1;
+    int recty1;
+    int rectx2;
+    int recty2;
+
+    if (!rect || !X1 || !Y1 || !X2 || !Y2) {
+        SDL_FALSE;
+    }
+
+    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;
+    }
+
+    /* Check to see if entire line is outside rect */
+    if ((x1 < rectx1 && x2 < rectx1) || (x1 > rectx2 && x2 > rectx2) ||
+        (y1 < recty1 && y2 < recty2) || (y1 > recty2 && y2 > recty2)) {
+        return SDL_FALSE;
+    }
+
+    if (y1 = y2) {
+        /* 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;
+    }
+
+    /* FIXME: need code to clip diagonal line to rect */
+    return SDL_FALSE;
+}
+
 void
 SDL_AddDirtyRect(SDL_DirtyRectList * list, const SDL_Rect * rect)
 {