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[Feat] (Tessellation): implement glPatchParameterfv and bake the default levels into both pass-through control stages

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Swung0x48
2026-08-27 02:11:19 -04:00
parent 0f2fcbc469
commit d5286e69b6
21 changed files with 546 additions and 64 deletions
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MobileGL/MG_Backend/DirectVulkan/Renderer/ProgramFactory.cpp
+62 -21
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@@ -13,7 +13,10 @@
#include "MG_Util/ShaderTranspiler/SpvcSession.h"
#include "MG_Util/ShaderTranspiler/Types.h"
#include <algorithm>
#include <bit>
#include <cmath>
#include <cstring>
#include <format>
#include <map>
#include <utility>
#include <spirv-tools/libspirv.h>
@@ -3594,18 +3597,48 @@ namespace MobileGL::MG_Backend::DirectVulkan {
}
}
String ProgramFactory::BuildPassthroughTessControlSource(Uint32 patchVertices) {
namespace {
// A GLSL float literal for a tessellation level. Always spelled with a decimal point,
// because an integral value written without one is an INT literal and
// `gl_TessLevelOuter[0] = 1;` does not compile. A non-finite value is baked as 0.0:
// glPatchParameterfv accepts any float, and a level that is not a positive number
// discards the patch - which is what a NaN level does in GL too - whereas emitting "nan"
// would make the synthesized stage fail to compile and take the whole program down.
String TessLevelLiteral(Float value) {
if (!std::isfinite(value)) return "0.0";
return std::format("{:.6f}", value);
}
} // namespace
Uint64 ProgramFactory::ComputePassthroughTessControlKey(Uint32 patchVertices,
const FloatVec4& defaultOuterLevel,
const FloatVec2& defaultInnerLevel) {
// A plain 28-byte blob of exactly what the generator reads, hashed once. Deliberately over
// the RAW BITS rather than the values: two levels that compare unequal must key apart, and
// a NaN level - which glPatchParameterfv accepts - compares unequal to itself.
struct Blob {
Uint32 patchVertices;
Uint32 outerBits[4];
Uint32 innerBits[2];
} blob{};
blob.patchVertices = patchVertices;
for (Uint32 i = 0; i < 4; ++i) blob.outerBits[i] = std::bit_cast<Uint32>(defaultOuterLevel[i]);
for (Uint32 i = 0; i < 2; ++i) blob.innerBits[i] = std::bit_cast<Uint32>(defaultInnerLevel[i]);
return XXH64(&blob, sizeof(blob), 0);
}
String ProgramFactory::BuildPassthroughTessControlSource(Uint32 patchVertices,
const FloatVec4& defaultOuterLevel,
const FloatVec2& defaultInnerLevel) {
// The stage GL 4.6 core 11.2.2 describes when a program has an evaluation shader and no
// control shader: "the input patch is passed through unmodified", the output patch has
// as many vertices as the input one (PATCH_VERTICES), and the levels come from the
// PATCH_DEFAULT_OUTER_LEVEL / PATCH_DEFAULT_INNER_LEVEL state.
//
// Those two levels default to 1.0 and are baked here as literals because
// glPatchParameterfv - their only setter - is not implemented in this frontend (it is a
// stub in MG_Impl/GLImpl/Exporting/Definitions.cpp). Implementing that entry point means
// making the levels a parameter of this source AND of the cache key in
// GetOrCreatePassthroughTessControlStage; the two must move together, so they are named
// together here.
// Those two levels are baked in as literals - Vulkan has no equivalent dynamic state, so
// compiling them in is the only way to honour glPatchParameterfv. That makes them part of
// this module's identity: GetOrCreatePassthroughTessControlStage keys its cache on them,
// and PipelineFactory hashes them into the pipeline key. The three must move together.
//
// gl_out carries gl_Position and nothing else on purpose. The evaluation stage that
// reads it was linked against the VERTEX stage directly, so its input gl_PerVertex holds
@@ -3648,20 +3681,28 @@ namespace MobileGL::MG_Backend::DirectVulkan {
"} gl_out[];\n";
source += "void main() {\n";
source += " gl_out[gl_InvocationID].gl_Position = gl_in[gl_InvocationID].gl_Position;\n";
source += " gl_TessLevelOuter[0] = 1.0;\n";
source += " gl_TessLevelOuter[1] = 1.0;\n";
source += " gl_TessLevelOuter[2] = 1.0;\n";
source += " gl_TessLevelOuter[3] = 1.0;\n";
source += " gl_TessLevelInner[0] = 1.0;\n";
source += " gl_TessLevelInner[1] = 1.0;\n";
for (Uint32 i = 0; i < 4; ++i) {
source += " gl_TessLevelOuter[" + std::to_string(i) +
"] = " + TessLevelLiteral(defaultOuterLevel[i]) + ";\n";
}
for (Uint32 i = 0; i < 2; ++i) {
source += " gl_TessLevelInner[" + std::to_string(i) +
"] = " + TessLevelLiteral(defaultInnerLevel[i]) + ";\n";
}
source += "}\n";
return source;
}
VkPipelineShaderStageCreateInfo ProgramFactory::GetOrCreatePassthroughTessControlStage(Uint32 patchVertices) {
VkPipelineShaderStageCreateInfo ProgramFactory::GetOrCreatePassthroughTessControlStage(
Uint32 patchVertices, const FloatVec4& defaultOuterLevel, const FloatVec2& defaultInnerLevel) {
// Everything compiled into the stage, folded into one key. The patch size alone stopped
// being enough once glPatchParameterfv could change the levels: two modules that differ
// only in a baked-in level are different modules, and pipelines built from either may be
// alive at the same time.
const Uint64 key = ComputePassthroughTessControlKey(patchVertices, defaultOuterLevel, defaultInnerLevel);
// A cached VK_NULL_HANDLE is a remembered failure, not a miss: returning it keeps a
// generator that cannot compile from re-running glslang on every draw.
const auto cached = m_passthroughTessControlStages.find(patchVertices);
const auto cached = m_passthroughTessControlStages.find(key);
if (cached != m_passthroughTessControlStages.end()) {
return cached->second;
}
@@ -3672,7 +3713,7 @@ namespace MobileGL::MG_Backend::DirectVulkan {
stage.pName = "main";
using namespace MG_Util::ShaderTranspiler;
const String source = BuildPassthroughTessControlSource(patchVertices);
const String source = BuildPassthroughTessControlSource(patchVertices, defaultOuterLevel, defaultInnerLevel);
// Same compile configuration as every other stage of every other program: this runs on
// the GL thread (the draw path), so the live compile env is the right one, and flags=0
// is the Vulkan-targeting form (CompileForOpenGL is what the GLES backend adds).
@@ -3686,7 +3727,7 @@ namespace MobileGL::MG_Backend::DirectVulkan {
MGLOG_E("ProgramFactory: could not compile the pass-through tessellation control stage for "
"patchVertices=%u; a program with an evaluation stage and no control stage cannot draw. %s",
patchVertices, compiled.error().log.c_str());
m_passthroughTessControlStages.emplace(patchVertices, stage);
m_passthroughTessControlStages.emplace(key, stage);
return stage;
}
@@ -3696,7 +3737,7 @@ namespace MobileGL::MG_Backend::DirectVulkan {
if (!linked) {
MGLOG_E("ProgramFactory: could not link the pass-through tessellation control stage for "
"patchVertices=%u. %s", patchVertices, linked.error().log.c_str());
m_passthroughTessControlStages.emplace(patchVertices, stage);
m_passthroughTessControlStages.emplace(key, stage);
return stage;
}
@@ -3705,7 +3746,7 @@ namespace MobileGL::MG_Backend::DirectVulkan {
if (!binary || binary.value().empty() || binary.value().front().empty()) {
MGLOG_E("ProgramFactory: could not generate SPIR-V for the pass-through tessellation control stage "
"for patchVertices=%u", patchVertices);
m_passthroughTessControlStages.emplace(patchVertices, stage);
m_passthroughTessControlStages.emplace(key, stage);
return stage;
}
@@ -3727,14 +3768,14 @@ namespace MobileGL::MG_Backend::DirectVulkan {
if (result != VK_SUCCESS) {
MGLOG_E("ProgramFactory: vkCreateShaderModule failed (%d) for the pass-through tessellation control "
"stage for patchVertices=%u", static_cast<Int>(result), patchVertices);
m_passthroughTessControlStages.emplace(patchVertices, stage);
m_passthroughTessControlStages.emplace(key, stage);
return stage;
}
stage.module = module;
MGLOG_D("ProgramFactory: built the pass-through tessellation control stage for patchVertices=%u "
"(GL 4.6 11.2.2; Vulkan has no fixed-function equivalent)", patchVertices);
m_passthroughTessControlStages.emplace(patchVertices, stage);
m_passthroughTessControlStages.emplace(key, stage);
return stage;
}