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IndexGenerator: Fix off-by-one in GetRemainingIndices

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Fixes https://bugs.dolphin-emu.org/issues/13136.
This commit is contained in:
Pokechu22 2023-01-02 19:23:31 -08:00
parent 6c58ba353c
commit cefcd9c93c
1 changed files with 11 additions and 3 deletions
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14
Source/Core/VideoCommon/IndexGenerator.cpp
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@ -328,13 +328,21 @@ void IndexGenerator::AddExternalIndices(const u16* indices, u32 num_indices, u32
u32 IndexGenerator::GetRemainingIndices(OpcodeDecoder::Primitive primitive) const
{
u32 max_index = USHRT_MAX;
u32 max_index = UINT16_MAX;
if (g_Config.UseVSForLinePointExpand() && primitive >= OpcodeDecoder::Primitive::GX_DRAW_LINES)
max_index >>= 2;
// -1 is reserved for primitive restart
max_index = max_index - 1;
// Although we reserve UINT16_MAX for primitive restart, we aren't allowed to use that as an
// actual index. But, the maximum number of vertices a game can send is UINT16_MAX, so up to
// 0xffff indices will be used by the game. These indices would be 0x0000 through 0xfffe,
// and since m_base_index gets incremented for each index used, after that m_base_index
// would be 0xffff and no indices remain. If a game uses 0xfffe vertices, assuming m_base_index
// started at 0 it would end at 0xfffe and one more index could be used. So, we do not need to
// subtract 1 from max_index to correctly reserve one index for primitive restart.
//
// Pocoyo Racing uses a draw command with 0xffff vertices, which previously caused issues; see
// https://bugs.dolphin-emu.org/issues/13136 for details.
if (m_base_index > max_index) [[unlikely]]
{