- // Take the last sample of the quanization block
- const int64_t final_index =
- min((i - (i % quantization_length) +
- quantization_length - 1), end);
-
- // Store the final state
- const bool final_sample = get_sample(final_index) & sig_mask;
- edges.push_back(pair<int64_t, bool>(
- final_index, final_sample));
-
- // Continue to sampling
- i = final_index;
- last_sample = final_sample;
+ // If resolution is less than a mip map block,
+ // round up to the beginning of the mip-map block
+ // for this level of detail
+ const int min_level_scale_power =
+ (level + 1) * MipMapScalePower;
+ index = pow2_ceil(index, min_level_scale_power);
+ if(index >= end)
+ break;
+
+ // We can fast forward only if there was no change
+ const bool sample =
+ (get_sample(index) & sig_mask) != 0;
+ fast_forward = last_sample == sample;
+ }
+
+ if(fast_forward) {
+
+ // Fast forward: This involves zooming out to higher
+ // levels of the mip map searching for changes, then
+ // zooming in on them to find the point where the edge
+ // begins.
+
+ // Slide right and zoom out at the beginnings of mip-map
+ // blocks until we encounter a change
+ while(1) {
+ const int level_scale_power =
+ (level + 1) * MipMapScalePower;
+ const uint64_t offset =
+ index >> level_scale_power;
+ assert(offset >= 0);
+
+ // Check if we reached the last block at this
+ // level, or if there was a change in this block
+ if(offset >= _mip_map[level].length ||
+ (get_subsample(level, offset) &
+ sig_mask))
+ break;
+
+ if((offset & ~(~0 << MipMapScalePower)) == 0) {
+ // If we are now at the beginning of a
+ // higher level mip-map block ascend one
+ // level
+ if(level + 1 >= ScaleStepCount ||
+ !_mip_map[level + 1].data)
+ break;
+
+ level++;
+ } else {
+ // Slide right to the beginning of the
+ // next mip map block
+ index = pow2_ceil(index + 1,
+ level_scale_power);
+ }
+ }
+
+ // Zoom in, and slide right until we encounter a change,
+ // and repeat until we reach min_level
+ while(1) {
+ assert(_mip_map[level].data);
+
+ const int level_scale_power =
+ (level + 1) * MipMapScalePower;
+ const uint64_t offset =
+ index >> level_scale_power;
+ assert(offset >= 0);
+
+ // Check if we reached the last block at this
+ // level, or if there was a change in this block
+ if(offset >= _mip_map[level].length ||
+ (get_subsample(level, offset) &
+ sig_mask)) {
+ // Zoom in unless we reached the minimum
+ // zoom
+ if(level == min_level)
+ break;
+
+ level--;
+ } else {
+ // Slide right to the beginning of the
+ // next mip map block
+ index = pow2_ceil(index + 1,
+ level_scale_power);
+ }
+ }
+
+ // If individual samples within the limit of resolution,
+ // do a linear search for the next transition within the
+ // block
+ if(min_length < MipMapScaleFactor) {
+ for(index; index < end; index++) {
+ const bool sample = (get_sample(index) &
+ sig_mask) != 0;
+ if(sample != last_sample)
+ break;
+ }
+ }