//split all existing clip rectangles against the passed rect
void Context_subtract_clip_rect(Context* context, Rect* subtracted_rect) {
//Check each item already in the list to see if it overlaps with
//the new rectangle
int i, j;
Rect* cur_rect;
List* split_rects;
context->clipping_on = 1;
for(i = 0; i < context->clip_rects->count; ) {
cur_rect = (Rect*)List_get_at(context->clip_rects, i);
//Standard rect intersect test (if no intersect, skip to next)
//see here for an example of why this works:
//http://stackoverflow.com/questions/306316/determine-if-two-rectangles-overlap-each-other#tab-top
if(!(cur_rect->left <= subtracted_rect->right &&
cur_rect->right >= subtracted_rect->left &&
cur_rect->top <= subtracted_rect->bottom &&
cur_rect->bottom >= subtracted_rect->top)) {
i++;
continue;
}
//If this rectangle does intersect with the new rectangle,
//we need to split it
List_remove_at(context->clip_rects, i); //Original will be replaced w/splits
split_rects = Rect_split(cur_rect, subtracted_rect); //Do the split
Object_delete((Object*)cur_rect); //We can throw this away now, we're done with it
//Copy the split, non-overlapping result rectangles into the list
while(split_rects->count) {
cur_rect = (Rect*)List_remove_at(split_rects, 0);
List_add(context->clip_rects, (Object*)cur_rect);
}
//Free the empty split_rect list
Object_delete((Object*)split_rects);
//Since we removed an item from the list, we need to start counting over again
//In this way, we'll only exit this loop once nothing in the list overlaps
i = 0;
}
}
//Remove all of the clipping rects from the passed context object
void Context_clear_clip_rects(Context* context) {
Rect* cur_rect;
context->clipping_on = 0;
while(context->clip_rects->count)
Object_delete(List_remove_at(context->clip_rects, 0));
}
List* Rect_split(Rect subject_rect, Rect cutting_rect) {
//Allocate the list of result rectangles
List* output_rects;
if(!(output_rects = List_new()))
return output_rects;
Rect subject_copy = subject_rect;
//We need a rectangle to hold new rectangles before
//they get pushed into the output list
Rect* temp_rect;
//Begin splitting
//1 -Split by left edge if that edge is between the subject's left and right edges
if(rect_min_x(cutting_rect) > rect_min_x(subject_copy) && rect_min_x(cutting_rect) <= rect_max_x(subject_copy)) {
//Try to make a new rectangle spanning from the subject rectangle's left and stopping before
//the cutting rectangle's left
if(!(temp_rect = Rect_new(rect_min_y(subject_copy), rect_min_x(subject_copy),
rect_max_y(subject_copy), rect_min_x(cutting_rect) - 1))) {
//If the object creation failed, we need to delete the list and exit failed
kfree(output_rects);
return (List*)0;
}
//Add the new rectangle to the output list
List_add(output_rects, temp_rect);
//Shrink the subject rectangle to exclude the split portion
int diff = rect_min_x(cutting_rect) - rect_min_x(subject_copy);
rect_min_x(subject_copy) += diff;
subject_copy.size.width -= diff;
}
//2 -Split by top edge if that edge is between the subject's top and bottom edges
if(rect_min_y(cutting_rect) > rect_min_y(subject_copy) && rect_min_y(cutting_rect) <= rect_max_y(subject_copy)) {
//Try to make a new rectangle spanning from the subject rectangle's top and stopping before
//the cutting rectangle's top
if(!(temp_rect = Rect_new(rect_min_y(subject_copy), rect_min_x(subject_copy),
rect_min_y(cutting_rect) - 1, rect_max_x(subject_copy)))) {
//If the object creation failed, we need to delete the list and exit failed
//This time, also delete any previously allocated rectangles
for(; output_rects->count; temp_rect = List_remove_at(output_rects, 0))
kfree(temp_rect);
kfree(output_rects);
return (List*)0;
}
//Add the new rectangle to the output list
List_add(output_rects, temp_rect);
//Shrink the subject rectangle to exclude the split portion
int diff = rect_min_y(cutting_rect) - rect_min_y(subject_copy);
rect_min_y(subject_copy) += diff;
subject_copy.size.height -= diff;
}
//3 -Split by right edge if that edge is between the subject's left and right edges
if(rect_max_x(cutting_rect) >= rect_min_x(subject_copy) && rect_max_x(cutting_rect) < rect_max_x(subject_copy)) {
//Try to make a new rectangle spanning from the subject rectangle's right and stopping before
//the cutting rectangle's right
if(!(temp_rect = Rect_new(rect_min_y(subject_copy), rect_max_x(cutting_rect) + 1,
rect_max_y(subject_copy), rect_max_x(subject_copy)))) {
//Free on fail
for(; output_rects->count; temp_rect = List_remove_at(output_rects, 0))
kfree(temp_rect);
kfree(output_rects);
return (List*)0;
}
//Add the new rectangle to the output list
List_add(output_rects, temp_rect);
//Shrink the subject rectangle to exclude the split portion
int shrink_amount = rect_max_x(subject_copy) - rect_max_x(cutting_rect);
subject_copy.size.width -= shrink_amount;
}
//4 -Split by bottom edge if that edge is between the subject's top and bottom edges
if(rect_max_y(cutting_rect) >= rect_min_y(subject_copy) && rect_max_y(cutting_rect) < rect_max_y(subject_copy)) {
//Try to make a new rectangle spanning from the subject rectangle's bottom and stopping before
//the cutting rectangle's bottom
if(!(temp_rect = Rect_new(rect_max_y(cutting_rect) + 1, rect_min_x(subject_copy),
rect_max_y(subject_copy), rect_max_x(subject_copy)))) {
//Free on fail
for(; output_rects->count; temp_rect = List_remove_at(output_rects, 0))
kfree(temp_rect);
kfree(output_rects);
return (List*)0;
}
//Add the new rectangle to the output list
List_add(output_rects, temp_rect);
//Shrink the subject rectangle to exclude the split portion
int shrink_amount = rect_max_y(subject_copy) - rect_max_y(cutting_rect);
subject_copy.size.height -= shrink_amount;
}
//Finally, after all that, we can return the output rectangles
return output_rects;
}