From 340ef142c3794bf0a8137daa957cfb82843d69b1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=D0=91=D1=80=D0=B0=D0=BD=D0=B8=D0=BC=D0=B8=D1=80=20=D0=9A?=
 =?UTF-8?q?=D0=B0=D1=80=D0=B0=D1=9F=D0=B8=D1=9B?=
 <branimirkaradzic@gmail.com>
Date: Tue, 1 Sep 2026 16:22:18 -0700
Subject: [PATCH] Enable primitive restart for strip topologies.

---
 src/renderer_d3d12.cpp  | 15 +++++++++++++++
 src/renderer_gl.cpp     | 18 ++++++++++++++++++
 src/renderer_gl.h       |  4 ++++
 src/renderer_vk.cpp     |  8 +++++++-
 src/renderer_webgpu.cpp |  1 +
 5 files changed, 45 insertions(+), 1 deletion(-)

diff --git a/src/renderer_d3d12.cpp b/src/renderer_d3d12.cpp
index 55e046832..c19185ec1 100644
--- a/src/renderer_d3d12.cpp
+++ b/src/renderer_d3d12.cpp
@@ -3775,6 +3775,7 @@ namespace bgfx { namespace d3d12
 			, const VertexLayout** _layouts
 			, ProgramHandle _program
 			, uint8_t _numInstanceData
+			, bool _index32 = false
 			)
 		{
 			ProgramD3D12& program = m_program[_program.idx];
@@ -3856,6 +3857,7 @@ namespace bgfx { namespace d3d12
 			murmur.begin();
 			murmur.add(_state);
 			murmur.add(rgba);
+			murmur.add(_index32);
 			murmur.add(_stencil);
 			murmur.add(program.m_vsh->m_hash);
 			murmur.add(program.m_vsh->m_attrMask, sizeof(program.m_vsh->m_attrMask) );
@@ -3971,6 +3973,18 @@ namespace bgfx { namespace d3d12
 			uint8_t primIndex = uint8_t( (_state&BGFX_STATE_PT_MASK) >> BGFX_STATE_PT_SHIFT);
 			desc.PrimitiveTopologyType = s_primInfo[primIndex].m_topologyType;
 
+			const uint64_t pt = _state & BGFX_STATE_PT_MASK;
+			desc.IBStripCutValue = (false
+				|| BGFX_STATE_PT_TRISTRIP  == pt
+				|| BGFX_STATE_PT_LINESTRIP == pt
+				)
+				? (_index32
+						? D3D12_INDEX_BUFFER_STRIP_CUT_VALUE_0xFFFFFFFF
+						: D3D12_INDEX_BUFFER_STRIP_CUT_VALUE_0xFFFF
+						)
+				: D3D12_INDEX_BUFFER_STRIP_CUT_VALUE_DISABLED
+				;
+
 			if (isValid(m_fbh) )
 			{
 				const FrameBufferD3D12& frameBuffer = m_frameBuffers[m_fbh.idx];
@@ -9397,6 +9411,7 @@ namespace bgfx { namespace d3d12
 						, layouts
 						, key.m_program
 						, uint8_t(draw.m_instanceDataStride/16)
+						, isValid(draw.m_indexBuffer) && !draw.isIndex16()
 						);
 
 					if (currentBindIdx != bindIdx
diff --git a/src/renderer_gl.cpp b/src/renderer_gl.cpp
index 2e9e30009..397a6c23a 100644
--- a/src/renderer_gl.cpp
+++ b/src/renderer_gl.cpp
@@ -8194,6 +8194,11 @@ namespace bgfx { namespace gl
 		}
 		PrimInfo prim = s_primInfo[primIndex];
 
+		const bool primitiveRestartSupported = false
+			|| BX_ENABLED(BGFX_CONFIG_RENDERER_OPENGLES >= 30)
+			|| s_extension[Extension::ARB_ES3_compatibility].m_supported
+			;
+
 		GL_CHECK(glPolygonMode(GL_FRONT_AND_BACK
 			, _render->m_debug&BGFX_DEBUG_WIREFRAME
 			? GL_LINE
@@ -8867,6 +8872,19 @@ namespace bgfx { namespace gl
 					const uint64_t pt = newFlags&BGFX_STATE_PT_MASK;
 					primIndex = uint8_t(pt>>BGFX_STATE_PT_SHIFT);
 					prim = s_primInfo[primIndex];
+
+					if (primitiveRestartSupported)
+					{
+						if (BGFX_STATE_PT_TRISTRIP  == pt
+						||  BGFX_STATE_PT_LINESTRIP == pt)
+						{
+							GL_CHECK(glEnable(GL_PRIMITIVE_RESTART_FIXED_INDEX) );
+						}
+						else
+						{
+							GL_CHECK(glDisable(GL_PRIMITIVE_RESTART_FIXED_INDEX) );
+						}
+					}
 				}
 
 				bool programChanged = false;
diff --git a/src/renderer_gl.h b/src/renderer_gl.h
index 13872c39e..5b5361191 100644
--- a/src/renderer_gl.h
+++ b/src/renderer_gl.h
@@ -1181,6 +1181,10 @@ typedef double GLdouble;
 #	define GL_LINE_SMOOTH 0x0B20
 #endif // GL_LINE_SMOOTH
 
+#ifndef GL_PRIMITIVE_RESTART_FIXED_INDEX
+#	define GL_PRIMITIVE_RESTART_FIXED_INDEX 0x8D69
+#endif // GL_PRIMITIVE_RESTART_FIXED_INDEX
+
 #ifndef GL_TEXTURE_LOD_BIAS
 #	define GL_TEXTURE_LOD_BIAS 0x8501
 #endif // GL_TEXTURE_LOD_BIAS
diff --git a/src/renderer_vk.cpp b/src/renderer_vk.cpp
index d8f9f0458..99e2da28c 100644
--- a/src/renderer_vk.cpp
+++ b/src/renderer_vk.cpp
@@ -4153,7 +4153,13 @@ VK_IMPORT_DEVICE
 			inputAssemblyState.pNext = NULL;
 			inputAssemblyState.flags = 0;
 			inputAssemblyState.topology = s_primInfo[(_state&BGFX_STATE_PT_MASK) >> BGFX_STATE_PT_SHIFT].m_topology;
-			inputAssemblyState.primitiveRestartEnable = VK_FALSE;
+			inputAssemblyState.primitiveRestartEnable = (false
+				|| VK_PRIMITIVE_TOPOLOGY_TRIANGLE_STRIP == inputAssemblyState.topology
+				|| VK_PRIMITIVE_TOPOLOGY_LINE_STRIP     == inputAssemblyState.topology
+				)
+				? VK_TRUE
+				: VK_FALSE
+				;
 
 			VkPipelineRasterizationStateCreateInfo rasterizationState;
 			setRasterizerState(rasterizationState, _state, m_wireframe);
diff --git a/src/renderer_webgpu.cpp b/src/renderer_webgpu.cpp
index 695556569..441f3d6ab 100644
--- a/src/renderer_webgpu.cpp
+++ b/src/renderer_webgpu.cpp
@@ -3195,6 +3195,7 @@ WGPU_IMPORT
 			murmur.add(layout.m_attributes, sizeof(layout.m_attributes) );
 			murmur.add(_msaaCount);
 			murmur.add(_numInstanceData);
+			murmur.add(_isIndex16);
 			murmur.add(_useDepthAttachment);
 			addAttachmentState(murmur, fb);
 			const uint32_t hash = murmur.end();