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Diffstat (limited to 'thirdparty/meshoptimizer/stripifier.cpp')
| -rw-r--r-- | thirdparty/meshoptimizer/stripifier.cpp | 295 |
1 files changed, 295 insertions, 0 deletions
diff --git a/thirdparty/meshoptimizer/stripifier.cpp b/thirdparty/meshoptimizer/stripifier.cpp new file mode 100644 index 0000000000..8ce17ef3dc --- /dev/null +++ b/thirdparty/meshoptimizer/stripifier.cpp @@ -0,0 +1,295 @@ +// This file is part of meshoptimizer library; see meshoptimizer.h for version/license details +#include "meshoptimizer.h" + +#include <assert.h> +#include <limits.h> +#include <string.h> + +// This work is based on: +// Francine Evans, Steven Skiena and Amitabh Varshney. Optimizing Triangle Strips for Fast Rendering. 1996 +namespace meshopt +{ + +static unsigned int findStripFirst(const unsigned int buffer[][3], unsigned int buffer_size, const unsigned int* valence) +{ + unsigned int index = 0; + unsigned int iv = ~0u; + + for (size_t i = 0; i < buffer_size; ++i) + { + unsigned int va = valence[buffer[i][0]], vb = valence[buffer[i][1]], vc = valence[buffer[i][2]]; + unsigned int v = (va < vb && va < vc) ? va : (vb < vc) ? vb : vc; + + if (v < iv) + { + index = unsigned(i); + iv = v; + } + } + + return index; +} + +static int findStripNext(const unsigned int buffer[][3], unsigned int buffer_size, unsigned int e0, unsigned int e1) +{ + for (size_t i = 0; i < buffer_size; ++i) + { + unsigned int a = buffer[i][0], b = buffer[i][1], c = buffer[i][2]; + + if (e0 == a && e1 == b) + return (int(i) << 2) | 2; + else if (e0 == b && e1 == c) + return (int(i) << 2) | 0; + else if (e0 == c && e1 == a) + return (int(i) << 2) | 1; + } + + return -1; +} + +} // namespace meshopt + +size_t meshopt_stripify(unsigned int* destination, const unsigned int* indices, size_t index_count, size_t vertex_count, unsigned int restart_index) +{ + assert(destination != indices); + assert(index_count % 3 == 0); + + using namespace meshopt; + + meshopt_Allocator allocator; + + const size_t buffer_capacity = 8; + + unsigned int buffer[buffer_capacity][3] = {}; + unsigned int buffer_size = 0; + + size_t index_offset = 0; + + unsigned int strip[2] = {}; + unsigned int parity = 0; + + size_t strip_size = 0; + + // compute vertex valence; this is used to prioritize starting triangle for strips + unsigned int* valence = allocator.allocate<unsigned int>(vertex_count); + memset(valence, 0, vertex_count * sizeof(unsigned int)); + + for (size_t i = 0; i < index_count; ++i) + { + unsigned int index = indices[i]; + assert(index < vertex_count); + + valence[index]++; + } + + int next = -1; + + while (buffer_size > 0 || index_offset < index_count) + { + assert(next < 0 || (size_t(next >> 2) < buffer_size && (next & 3) < 3)); + + // fill triangle buffer + while (buffer_size < buffer_capacity && index_offset < index_count) + { + buffer[buffer_size][0] = indices[index_offset + 0]; + buffer[buffer_size][1] = indices[index_offset + 1]; + buffer[buffer_size][2] = indices[index_offset + 2]; + + buffer_size++; + index_offset += 3; + } + + assert(buffer_size > 0); + + if (next >= 0) + { + unsigned int i = next >> 2; + unsigned int a = buffer[i][0], b = buffer[i][1], c = buffer[i][2]; + unsigned int v = buffer[i][next & 3]; + + // ordered removal from the buffer + memmove(buffer[i], buffer[i + 1], (buffer_size - i - 1) * sizeof(buffer[0])); + buffer_size--; + + // update vertex valences for strip start heuristic + valence[a]--; + valence[b]--; + valence[c]--; + + // find next triangle (note that edge order flips on every iteration) + // in some cases we need to perform a swap to pick a different outgoing triangle edge + // for [a b c], the default strip edge is [b c], but we might want to use [a c] + int cont = findStripNext(buffer, buffer_size, parity ? strip[1] : v, parity ? v : strip[1]); + int swap = cont < 0 ? findStripNext(buffer, buffer_size, parity ? v : strip[0], parity ? strip[0] : v) : -1; + + if (cont < 0 && swap >= 0) + { + // [a b c] => [a b a c] + destination[strip_size++] = strip[0]; + destination[strip_size++] = v; + + // next strip has same winding + // ? a b => b a v + strip[1] = v; + + next = swap; + } + else + { + // emit the next vertex in the strip + destination[strip_size++] = v; + + // next strip has flipped winding + strip[0] = strip[1]; + strip[1] = v; + parity ^= 1; + + next = cont; + } + } + else + { + // if we didn't find anything, we need to find the next new triangle + // we use a heuristic to maximize the strip length + unsigned int i = findStripFirst(buffer, buffer_size, &valence[0]); + unsigned int a = buffer[i][0], b = buffer[i][1], c = buffer[i][2]; + + // ordered removal from the buffer + memmove(buffer[i], buffer[i + 1], (buffer_size - i - 1) * sizeof(buffer[0])); + buffer_size--; + + // update vertex valences for strip start heuristic + valence[a]--; + valence[b]--; + valence[c]--; + + // we need to pre-rotate the triangle so that we will find a match in the existing buffer on the next iteration + int ea = findStripNext(buffer, buffer_size, c, b); + int eb = findStripNext(buffer, buffer_size, a, c); + int ec = findStripNext(buffer, buffer_size, b, a); + + // in some cases we can have several matching edges; since we can pick any edge, we pick the one with the smallest + // triangle index in the buffer. this reduces the effect of stripification on ACMR and additionally - for unclear + // reasons - slightly improves the stripification efficiency + int mine = INT_MAX; + mine = (ea >= 0 && mine > ea) ? ea : mine; + mine = (eb >= 0 && mine > eb) ? eb : mine; + mine = (ec >= 0 && mine > ec) ? ec : mine; + + if (ea == mine) + { + // keep abc + next = ea; + } + else if (eb == mine) + { + // abc -> bca + unsigned int t = a; + a = b, b = c, c = t; + + next = eb; + } + else if (ec == mine) + { + // abc -> cab + unsigned int t = c; + c = b, b = a, a = t; + + next = ec; + } + + if (restart_index) + { + if (strip_size) + destination[strip_size++] = restart_index; + + destination[strip_size++] = a; + destination[strip_size++] = b; + destination[strip_size++] = c; + + // new strip always starts with the same edge winding + strip[0] = b; + strip[1] = c; + parity = 1; + } + else + { + if (strip_size) + { + // connect last strip using degenerate triangles + destination[strip_size++] = strip[1]; + destination[strip_size++] = a; + } + + // note that we may need to flip the emitted triangle based on parity + // we always end up with outgoing edge "cb" in the end + unsigned int e0 = parity ? c : b; + unsigned int e1 = parity ? b : c; + + destination[strip_size++] = a; + destination[strip_size++] = e0; + destination[strip_size++] = e1; + + strip[0] = e0; + strip[1] = e1; + parity ^= 1; + } + } + } + + return strip_size; +} + +size_t meshopt_stripifyBound(size_t index_count) +{ + assert(index_count % 3 == 0); + + // worst case without restarts is 2 degenerate indices and 3 indices per triangle + // worst case with restarts is 1 restart index and 3 indices per triangle + return (index_count / 3) * 5; +} + +size_t meshopt_unstripify(unsigned int* destination, const unsigned int* indices, size_t index_count, unsigned int restart_index) +{ + assert(destination != indices); + + size_t offset = 0; + size_t start = 0; + + for (size_t i = 0; i < index_count; ++i) + { + if (restart_index && indices[i] == restart_index) + { + start = i + 1; + } + else if (i - start >= 2) + { + unsigned int a = indices[i - 2], b = indices[i - 1], c = indices[i]; + + // flip winding for odd triangles + if ((i - start) & 1) + { + unsigned int t = a; + a = b, b = t; + } + + // although we use restart indices, strip swaps still produce degenerate triangles, so skip them + if (a != b && a != c && b != c) + { + destination[offset + 0] = a; + destination[offset + 1] = b; + destination[offset + 2] = c; + offset += 3; + } + } + } + + return offset; +} + +size_t meshopt_unstripifyBound(size_t index_count) +{ + assert(index_count == 0 || index_count >= 3); + + return (index_count == 0) ? 0 : (index_count - 2) * 3; +} |