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thorvg/src/renderer/tvgRender.cpp
Hermet Park 07331eb76c renderer: add partial rendering support 
Partial Rendering refers to a rendering technique where
only a portion of the scene or screen is updated, rather
than redrawing the entire output. It is commonly used as
a performance optimization strategy, focusing on redrawing
only the regions that have changed, often called dirty regions.

This introduces RenderDirtyRegion, which assists
in collecting a compact dirty region from render tasks.

To efficient data-processing, this divide the screen region
with a designated size of partition and handles the partitl rendering
computation with a divide-conquer metholodgy.

Each backend can utilize this class to support efficient partial rendering.
This is implemented using a Line Sweep and Subdivision Merging O(NlogN).

The basic per-frame workflow is as follows:

0. RenderDirtyRegion::init() //set the screen size to properly partition the regions
1. RenderDirtyRegion::prepare() //Call this in Renderer::preRender().
2. RenderDirtyRegion::add() //Add all dirty paints for the frame before rendering.
3. RenderDirtyRegion::commit() //Generate the partial rendering region list before rendering.
4. RenderDirtyRegion::partition() //Get a certian partition
5. RenderDirtyRegion::get() //Retrieve the current dirty region list of a partition and use it when drawing paints.
6. RenderDirtyRegion::clear() //Reset the state.

RenderMethod introduced for 2 utilities for paritial renderings

1. RenderMethod::damage() //add a force dirty region, especially useful for scene effects
2. RenderMethod::partial() //toggle the partial rendering feature

issue: https://github.com/thorvg/thorvg/issues/1747
2025-06-23 16:04:48 +09:00

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/*
* Copyright (c) 2020 - 2025 the ThorVG project. All rights reserved.
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
* The above copyright notice and this permission notice shall be included in all
* copies or substantial portions of the Software.
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
#include <algorithm>
#include "tvgMath.h"
#include "tvgRender.h"
/************************************************************************/
/* RenderMethod Class Implementation */
/************************************************************************/
uint32_t RenderMethod::ref()
{
ScopedLock lock(key);
return (++refCnt);
}
uint32_t RenderMethod::unref()
{
ScopedLock lock(key);
return (--refCnt);
}
RenderRegion RenderMethod::viewport()
{
return vport;
}
bool RenderMethod::viewport(const RenderRegion& vp)
{
vport = vp;
return true;
}
/************************************************************************/
/* RenderPath Class Implementation */
/************************************************************************/
bool RenderPath::bounds(Matrix* m, float* x, float* y, float* w, float* h)
{
//unexpected
if (cmds.empty() || cmds.first() == PathCommand::CubicTo) return false;
auto min = Point{FLT_MAX, FLT_MAX};
auto max = Point{-FLT_MAX, -FLT_MAX};
auto pt = pts.begin();
auto cmd = cmds.begin();
auto assign = [&](const Point& pt, Point& min, Point& max) -> void {
if (pt.x < min.x) min.x = pt.x;
if (pt.y < min.y) min.y = pt.y;
if (pt.x > max.x) max.x = pt.x;
if (pt.y > max.y) max.y = pt.y;
};
while (cmd < cmds.end()) {
switch (*cmd) {
case PathCommand::MoveTo: {
//skip the invalid assignments
if (cmd + 1 < cmds.end()) {
auto next = *(cmd + 1);
if (next == PathCommand::LineTo || next == PathCommand::CubicTo) {
assign(*pt * m, min, max);
}
}
++pt;
break;
}
case PathCommand::LineTo: {
assign(*pt * m, min, max);
++pt;
break;
}
case PathCommand::CubicTo: {
Bezier bz = {pt[-1] * m, pt[0] * m, pt[1] * m, pt[2] * m};
bz.bounds(min, max);
pt += 3;
break;
}
default: break;
}
++cmd;
}
if (x) *x = min.x;
if (y) *y = min.y;
if (w) *w = max.x - min.x;
if (h) *h = max.y - min.y;
return true;
}
/************************************************************************/
/* RenderRegion Class Implementation */
/************************************************************************/
void RenderRegion::intersect(const RenderRegion& rhs)
{
if (min.x < rhs.min.x) min.x = rhs.min.x;
if (min.y < rhs.min.y) min.y = rhs.min.y;
if (max.x > rhs.max.x) max.x = rhs.max.x;
if (max.y > rhs.max.y) max.y = rhs.max.y;
// Not intersected: collapse to zero-area region
if (max.x < min.x) max.x = min.x;
if (max.y < min.y) max.y = min.y;
}
void RenderDirtyRegion::init(uint32_t w, uint32_t h)
{
auto cnt = int(sqrt(PARTITIONING));
auto px = int32_t(w / cnt);
auto py = int32_t(h / cnt);
auto lx = int32_t(w % cnt);
auto ly = int32_t(h % cnt);
//space partitioning
for (int y = 0; y < cnt; ++y) {
for (int x = 0; x < cnt; ++x) {
auto& partition = partitions[y * cnt + x];
partition.list[0].reserve(64);
auto& region = partition.region;
region.min = {x * px, y * py};
region.max = {region.min.x + px, region.min.y + py};
//leftovers
if (x == cnt -1) region.max.x += lx;
if (y == cnt -1) region.max.y += ly;
}
}
}
void RenderDirtyRegion::add(const RenderRegion* prv, const RenderRegion* cur)
{
if (disabled) return;
auto pvalid = prv ? prv->valid() : false;
auto cvalid = cur ? cur->valid() : false;
if (!pvalid && !cvalid) return;
for (int idx = 0; idx < PARTITIONING; ++idx) {
auto& partition = partitions[idx];
if (pvalid && prv->intersected(partition.region)) {
ScopedLock lock(key);
partition.list[partition.current].push(RenderRegion::intersect(*prv, partition.region));
}
if (cvalid && cur->intersected(partition.region)) {
ScopedLock lock(key);
partition.list[partition.current].push(RenderRegion::intersect(*cur, partition.region));
}
}
}
void RenderDirtyRegion::clear()
{
for (int idx = 0; idx < PARTITIONING; ++idx) {
partitions[idx].list[0].clear();
partitions[idx].list[1].clear();
}
}
void RenderDirtyRegion::subdivide(Array<RenderRegion>& targets, uint32_t idx, RenderRegion& lhs, RenderRegion& rhs)
{
RenderRegion temp[5];
int cnt = 0;
temp[cnt++] = RenderRegion::intersect(lhs, rhs);
auto max = std::min(lhs.max.x, rhs.max.x);
auto subtract = [&](RenderRegion& lhs, RenderRegion& rhs) {
//top
if (rhs.min.y < lhs.min.y) {
temp[cnt++] = {{rhs.min.x, rhs.min.y}, {rhs.max.x, lhs.min.y}};
rhs.min.y = lhs.min.y;
}
//bottom
if (rhs.max.y > lhs.max.y) {
temp[cnt++] = {{rhs.min.x, lhs.max.y}, {rhs.max.x, rhs.max.y}};
rhs.max.y = lhs.max.y;
}
//left
if (rhs.min.x < lhs.min.x) {
temp[cnt++] = {{rhs.min.x, rhs.min.y}, {lhs.min.x, rhs.max.y}};
rhs.min.x = lhs.min.x;
}
//right
if (rhs.max.x > lhs.max.x) {
temp[cnt++] = {{lhs.max.x, rhs.min.y}, {rhs.max.x, rhs.max.y}};
//rhs.max.x = lhs.max.x;
}
};
subtract(temp[0], lhs);
subtract(temp[0], rhs);
/* Considered using a list to avoid memory shifting,
but ultimately, the array outperformed the list due to better cache locality. */
//shift data
auto dst = &targets[idx + cnt];
memmove(dst, &targets[idx + 1], sizeof(RenderRegion) * (targets.count - idx - 1));
memcpy(&targets[idx], temp, sizeof(RenderRegion) * cnt);
targets.count += (cnt - 1);
//sorting by x coord again, only for the updated region
while (dst < targets.end() && dst->min.x < max) ++dst;
stable_sort(&targets[idx], dst, [](const RenderRegion& a, const RenderRegion& b) -> bool {
return a.min.x < b.min.x;
});
}
void RenderDirtyRegion::commit()
{
if (disabled) return;
for (int idx = 0; idx < PARTITIONING; ++idx) {
auto current = partitions[idx].current;
auto& targets = partitions[idx].list[current];
if (targets.empty()) return;
current = !current; //swapping buffers
auto& output = partitions[idx].list[current];
targets.reserve(targets.count * 5); //one intersection can be divided up to 5
output.reserve(targets.count);
partitions[idx].current = current;
//sorting by x coord. guarantee the stable performance: O(NlogN)
stable_sort(targets.begin(), targets.end(), [](const RenderRegion& a, const RenderRegion& b) -> bool {
return a.min.x < b.min.x;
});
//Optimized using sweep-line algorithm: O(NlogN)
for (uint32_t i = 0; i < targets.count; ++i) {
auto& lhs = targets[i];
if (lhs.invalid()) continue;
auto merged = false;
for (uint32_t j = i + 1; j < targets.count; ++j) {
auto& rhs = targets[j];
if (rhs.invalid()) continue;
if (lhs.max.x < rhs.min.x) break; //line sweeping
//fully overlapped. drop lhs
if (rhs.contained(lhs)) {
merged = true;
break;
}
//fully overlapped. replace the lhs with rhs
if (lhs.contained(rhs)) {
rhs = {};
continue;
}
//just merge & expand on x axis
if (lhs.min.y == rhs.min.y && lhs.max.y == rhs.max.y) {
if (lhs.min.x <= rhs.max.x && rhs.min.x <= lhs.max.x) {
rhs.min.x = std::min(lhs.min.x, rhs.min.x);
rhs.max.x = std::max(lhs.max.x, rhs.max.x);
merged = true;
break;
}
}
//just merge & expand on y axis
if (lhs.min.x == rhs.min.x && lhs.max.x == rhs.max.x) {
if (lhs.min.y <= rhs.max.y && rhs.min.y < lhs.max.y) {
rhs.min.y = std::min(lhs.min.y, rhs.min.y);
rhs.max.y = std::max(lhs.max.y, rhs.max.y);
merged = true;
break;
}
}
//subdivide regions
if (lhs.intersected(rhs)) {
subdivide(targets, j, lhs, rhs);
merged = true;
break;
}
}
if (!merged) output.push(lhs); //this region is complete isolated
lhs = {};
}
}
}
/************************************************************************/
/* RenderTrimPath Class Implementation */
/************************************************************************/
#define EPSILON 1e-4f
static void _trimAt(const PathCommand* cmds, const Point* pts, Point& moveTo, float at1, float at2, bool start, RenderPath& out)
{
switch (*cmds) {
case PathCommand::LineTo: {
Line tmp, left, right;
Line{*(pts - 1), *pts}.split(at1, left, tmp);
tmp.split(at2, left, right);
if (start) {
out.pts.push(left.pt1);
moveTo = left.pt1;
out.cmds.push(PathCommand::MoveTo);
}
out.pts.push(left.pt2);
out.cmds.push(PathCommand::LineTo);
break;
}
case PathCommand::CubicTo: {
Bezier tmp, left, right;
Bezier{*(pts - 1), *pts, *(pts + 1), *(pts + 2)}.split(at1, left, tmp);
tmp.split(at2, left, right);
if (start) {
moveTo = left.start;
out.pts.push(left.start);
out.cmds.push(PathCommand::MoveTo);
}
out.pts.push(left.ctrl1);
out.pts.push(left.ctrl2);
out.pts.push(left.end);
out.cmds.push(PathCommand::CubicTo);
break;
}
case PathCommand::Close: {
Line tmp, left, right;
Line{*(pts - 1), moveTo}.split(at1, left, tmp);
tmp.split(at2, left, right);
if (start) {
moveTo = left.pt1;
out.pts.push(left.pt1);
out.cmds.push(PathCommand::MoveTo);
}
out.pts.push(left.pt2);
out.cmds.push(PathCommand::LineTo);
break;
}
default: break;
}
}
static void _add(const PathCommand* cmds, const Point* pts, const Point& moveTo, bool& start, RenderPath& out)
{
switch (*cmds) {
case PathCommand::MoveTo: {
out.cmds.push(PathCommand::MoveTo);
out.pts.push(*pts);
start = false;
break;
}
case PathCommand::LineTo: {
if (start) {
out.cmds.push(PathCommand::MoveTo);
out.pts.push(*(pts - 1));
}
out.cmds.push(PathCommand::LineTo);
out.pts.push(*pts);
start = false;
break;
}
case PathCommand::CubicTo: {
if (start) {
out.cmds.push(PathCommand::MoveTo);
out.pts.push(*(pts - 1));
}
out.cmds.push(PathCommand::CubicTo);
out.pts.push(*pts);
out.pts.push(*(pts + 1));
out.pts.push(*(pts + 2));
start = false;
break;
}
case PathCommand::Close: {
if (start) {
out.cmds.push(PathCommand::MoveTo);
out.pts.push(*(pts - 1));
}
out.cmds.push(PathCommand::LineTo);
out.pts.push(moveTo);
start = true;
break;
}
}
}
static void _trimPath(const PathCommand* inCmds, uint32_t inCmdsCnt, const Point* inPts, TVG_UNUSED uint32_t inPtsCnt, float trimStart, float trimEnd, RenderPath& out, bool connect = false)
{
auto cmds = const_cast<PathCommand*>(inCmds);
auto pts = const_cast<Point*>(inPts);
auto moveToTrimmed = *pts;
auto moveTo = *pts;
auto len = 0.0f;
auto _length = [&]() -> float {
switch (*cmds) {
case PathCommand::MoveTo: return 0.0f;
case PathCommand::LineTo: return tvg::length(pts - 1, pts);
case PathCommand::CubicTo: return Bezier{*(pts - 1), *pts, *(pts + 1), *(pts + 2)}.length();
case PathCommand::Close: return tvg::length(pts - 1, &moveTo);
}
return 0.0f;
};
auto _shift = [&]() -> void {
switch (*cmds) {
case PathCommand::MoveTo:
moveTo = *pts;
moveToTrimmed = *pts;
++pts;
break;
case PathCommand::LineTo:
++pts;
break;
case PathCommand::CubicTo:
pts += 3;
break;
case PathCommand::Close:
break;
}
++cmds;
};
auto start = !connect;
for (uint32_t i = 0; i < inCmdsCnt; ++i) {
auto dLen = _length();
//very short segments are skipped since due to the finite precision of Bezier curve subdivision and length calculation (1e-2),
//trimming may produce very short segments that would effectively have zero length with higher computational accuracy.
if (len <= trimStart) {
//cut the segment at the beginning and at the end
if (len + dLen > trimEnd) {
_trimAt(cmds, pts, moveToTrimmed, trimStart - len, trimEnd - trimStart, start, out);
start = false;
//cut the segment at the beginning
} else if (len + dLen > trimStart + EPSILON) {
_trimAt(cmds, pts, moveToTrimmed, trimStart - len, len + dLen - trimStart, start, out);
start = false;
}
} else if (len <= trimEnd - EPSILON) {
//cut the segment at the end
if (len + dLen > trimEnd) {
_trimAt(cmds, pts, moveTo, 0.0f, trimEnd - len, start, out);
start = true;
//add the whole segment
} else if (len + dLen > trimStart + EPSILON) _add(cmds, pts, moveTo, start, out);
}
len += dLen;
_shift();
}
}
static void _trim(const PathCommand* inCmds, uint32_t inCmdsCnt, const Point* inPts, uint32_t inPtsCnt, float begin, float end, bool connect, RenderPath& out)
{
auto totalLength = tvg::length(inCmds, inCmdsCnt, inPts, inPtsCnt);
auto trimStart = begin * totalLength;
auto trimEnd = end * totalLength;
if (begin >= end) {
_trimPath(inCmds, inCmdsCnt, inPts, inPtsCnt, trimStart, totalLength, out);
_trimPath(inCmds, inCmdsCnt, inPts, inPtsCnt, 0.0f, trimEnd, out, connect);
} else {
_trimPath(inCmds, inCmdsCnt, inPts, inPtsCnt, trimStart, trimEnd, out);
}
}
static void _get(float& begin, float& end)
{
auto loop = true;
if (begin > 1.0f && end > 1.0f) loop = false;
if (begin < 0.0f && end < 0.0f) loop = false;
if (begin >= 0.0f && begin <= 1.0f && end >= 0.0f && end <= 1.0f) loop = false;
if (begin > 1.0f) begin -= 1.0f;
if (begin < 0.0f) begin += 1.0f;
if (end > 1.0f) end -= 1.0f;
if (end < 0.0f) end += 1.0f;
if ((loop && begin < end) || (!loop && begin > end)) std::swap(begin, end);
}
bool RenderTrimPath::trim(const RenderPath& in, RenderPath& out) const
{
if (in.pts.count < 2 || tvg::zero(begin - end)) return false;
float begin = this->begin, end = this->end;
_get(begin, end);
out.cmds.reserve(in.cmds.count * 2);
out.pts.reserve(in.pts.count * 2);
auto pts = in.pts.data;
auto cmds = in.cmds.data;
if (simultaneous) {
auto startCmds = cmds;
auto startPts = pts;
uint32_t i = 0;
while (i < in.cmds.count) {
switch (in.cmds[i]) {
case PathCommand::MoveTo: {
if (startCmds != cmds) _trim(startCmds, cmds - startCmds, startPts, pts - startPts, begin, end, *(cmds - 1) == PathCommand::Close, out);
startPts = pts;
startCmds = cmds;
++pts;
++cmds;
break;
}
case PathCommand::LineTo: {
++pts;
++cmds;
break;
}
case PathCommand::CubicTo: {
pts += 3;
++cmds;
break;
}
case PathCommand::Close: {
++cmds;
if (startCmds != cmds) _trim(startCmds, cmds - startCmds, startPts, pts - startPts, begin, end, *(cmds - 1) == PathCommand::Close, out);
startPts = pts;
startCmds = cmds;
break;
}
}
i++;
}
if (startCmds != cmds) _trim(startCmds, cmds - startCmds, startPts, pts - startPts, begin, end, *(cmds - 1) == PathCommand::Close, out);
} else {
_trim(in.cmds.data, in.cmds.count, in.pts.data, in.pts.count, begin, end, false, out);
}
return out.pts.count >= 2;
}
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