MSL: Don't set the layer for multiview if the device doesn't support it.

Some older iOS devices don't support layered rendering. In that case,
don't set `[[render_target_array_index]]`, because the compiler will
reject the shader in that case. The client will then have to unroll the
render pass manually.

CMakeLists.txt

@@ -323,7 +323,7 @@ if (SPIRV_CROSS_STATIC)
 endif()
 
 set(spirv-cross-abi-major 0)
-set(spirv-cross-abi-minor 37)
+set(spirv-cross-abi-minor 38)
 set(spirv-cross-abi-patch 0)
 
 if (SPIRV_CROSS_SHARED)

main.cpp

@@ -549,6 +549,7 @@ struct CLIArguments
 	bool msl_invariant_float_math = false;
 	bool msl_emulate_cube_array = false;
 	bool msl_multiview = false;
+	bool msl_multiview_layered_rendering = true;
 	bool msl_view_index_from_device_index = false;
 	bool msl_dispatch_base = false;
 	bool msl_decoration_binding = false;
@@ -732,6 +733,8 @@ static void print_help_msl()
 	                "\t[--msl-device-argument-buffer <descriptor set index>]:\n\t\tUse device address space to hold indirect argument buffers instead of constant.\n"
 	                "\t\tComes up when trying to support argument buffers which are larger than 64 KiB.\n"
 	                "\t[--msl-multiview]:\n\t\tEnable SPV_KHR_multiview emulation.\n"
+	                "\t[--msl-multiview-no-layered-rendering]:\n\t\tDon't set [[render_target_array_index]] in multiview shaders.\n"
+	                "\t\tUseful for devices which don't support layered rendering. Only effective when --msl-multiview is enabled.\n"
 	                "\t[--msl-view-index-from-device-index]:\n\t\tTreat the view index as the device index instead.\n"
 	                "\t\tFor multi-GPU rendering.\n"
 	                "\t[--msl-dispatch-base]:\n\t\tAdd support for vkCmdDispatchBase() or similar APIs.\n"
@@ -987,6 +990,7 @@ static string compile_iteration(const CLIArguments &args, std::vector<uint32_t>
 		msl_opts.argument_buffers = args.msl_argument_buffers;
 		msl_opts.texture_buffer_native = args.msl_texture_buffer_native;
 		msl_opts.multiview = args.msl_multiview;
+		msl_opts.multiview_layered_rendering = args.msl_multiview_layered_rendering;
 		msl_opts.view_index_from_device_index = args.msl_view_index_from_device_index;
 		msl_opts.dispatch_base = args.msl_dispatch_base;
 		msl_opts.enable_decoration_binding = args.msl_decoration_binding;
@@ -1366,6 +1370,8 @@ static int main_inner(int argc, char *argv[])
 	cbs.add("--msl-invariant-float-math", [&args](CLIParser &) { args.msl_invariant_float_math = true; });
 	cbs.add("--msl-emulate-cube-array", [&args](CLIParser &) { args.msl_emulate_cube_array = true; });
 	cbs.add("--msl-multiview", [&args](CLIParser &) { args.msl_multiview = true; });
+	cbs.add("--msl-multiview-no-layered-rendering",
+	        [&args](CLIParser &) { args.msl_multiview_layered_rendering = false; });
 	cbs.add("--msl-view-index-from-device-index",
 	        [&args](CLIParser &) { args.msl_view_index_from_device_index = true; });
 	cbs.add("--msl-dispatch-base", [&args](CLIParser &) { args.msl_dispatch_base = true; });

reference/opt/shaders-msl/vulkan/frag/basic.multiview.no-layered.nocompat.vk.frag

@@ -0,0 +1,73 @@
+#pragma clang diagnostic ignored "-Wmissing-prototypes"
+#pragma clang diagnostic ignored "-Wmissing-braces"
+
+#include <metal_stdlib>
+#include <simd/simd.h>
+
+using namespace metal;
+
+template<typename T, size_t Num>
+struct spvUnsafeArray
+{
+    T elements[Num ? Num : 1];
+
+    thread T& operator [] (size_t pos) thread
+    {
+        return elements[pos];
+    }
+    constexpr const thread T& operator [] (size_t pos) const thread
+    {
+        return elements[pos];
+    }
+
+    device T& operator [] (size_t pos) device
+    {
+        return elements[pos];
+    }
+    constexpr const device T& operator [] (size_t pos) const device
+    {
+        return elements[pos];
+    }
+
+    constexpr const constant T& operator [] (size_t pos) const constant
+    {
+        return elements[pos];
+    }
+
+    threadgroup T& operator [] (size_t pos) threadgroup
+    {
+        return elements[pos];
+    }
+    constexpr const threadgroup T& operator [] (size_t pos) const threadgroup
+    {
+        return elements[pos];
+    }
+};
+
+struct main0_out
+{
+    float4 FragColor [[color(0)]];
+};
+
+struct main0_in
+{
+    float4 vColor [[user(locn0)]];
+    float2 vTex_0 [[user(locn1)]];
+    float2 vTex_1 [[user(locn2)]];
+    float2 vTex_2 [[user(locn3)]];
+    float2 vTex_3 [[user(locn4)]];
+};
+
+fragment main0_out main0(main0_in in [[stage_in]], constant uint* spvViewMask [[buffer(24)]], texture2d<float> uTex [[texture(0)]], sampler uTexSmplr [[sampler(0)]])
+{
+    main0_out out = {};
+    spvUnsafeArray<float2, 4> vTex = {};
+    vTex[0] = in.vTex_0;
+    vTex[1] = in.vTex_1;
+    vTex[2] = in.vTex_2;
+    vTex[3] = in.vTex_3;
+    const uint gl_ViewIndex = spvViewMask[0];
+    out.FragColor = in.vColor * uTex.sample(uTexSmplr, vTex[int(gl_ViewIndex)]);
+    return out;
+}
+

reference/opt/shaders-msl/vulkan/vert/multiview.multiview.no-layered.nocompat.vk.vert

@@ -0,0 +1,28 @@
+#include <metal_stdlib>
+#include <simd/simd.h>
+
+using namespace metal;
+
+struct MVPs
+{
+    float4x4 MVP[2];
+};
+
+struct main0_out
+{
+    float4 gl_Position [[position]];
+};
+
+struct main0_in
+{
+    float4 Position [[attribute(0)]];
+};
+
+vertex main0_out main0(main0_in in [[stage_in]], constant uint* spvViewMask [[buffer(24)]], constant MVPs& _19 [[buffer(0)]])
+{
+    main0_out out = {};
+    const uint gl_ViewIndex = spvViewMask[0];
+    out.gl_Position = _19.MVP[int(gl_ViewIndex)] * in.Position;
+    return out;
+}
+

reference/shaders-msl/vulkan/frag/basic.multiview.no-layered.nocompat.vk.frag

@@ -0,0 +1,73 @@
+#pragma clang diagnostic ignored "-Wmissing-prototypes"
+#pragma clang diagnostic ignored "-Wmissing-braces"
+
+#include <metal_stdlib>
+#include <simd/simd.h>
+
+using namespace metal;
+
+template<typename T, size_t Num>
+struct spvUnsafeArray
+{
+    T elements[Num ? Num : 1];
+
+    thread T& operator [] (size_t pos) thread
+    {
+        return elements[pos];
+    }
+    constexpr const thread T& operator [] (size_t pos) const thread
+    {
+        return elements[pos];
+    }
+
+    device T& operator [] (size_t pos) device
+    {
+        return elements[pos];
+    }
+    constexpr const device T& operator [] (size_t pos) const device
+    {
+        return elements[pos];
+    }
+
+    constexpr const constant T& operator [] (size_t pos) const constant
+    {
+        return elements[pos];
+    }
+
+    threadgroup T& operator [] (size_t pos) threadgroup
+    {
+        return elements[pos];
+    }
+    constexpr const threadgroup T& operator [] (size_t pos) const threadgroup
+    {
+        return elements[pos];
+    }
+};
+
+struct main0_out
+{
+    float4 FragColor [[color(0)]];
+};
+
+struct main0_in
+{
+    float4 vColor [[user(locn0)]];
+    float2 vTex_0 [[user(locn1)]];
+    float2 vTex_1 [[user(locn2)]];
+    float2 vTex_2 [[user(locn3)]];
+    float2 vTex_3 [[user(locn4)]];
+};
+
+fragment main0_out main0(main0_in in [[stage_in]], constant uint* spvViewMask [[buffer(24)]], texture2d<float> uTex [[texture(0)]], sampler uTexSmplr [[sampler(0)]])
+{
+    main0_out out = {};
+    spvUnsafeArray<float2, 4> vTex = {};
+    vTex[0] = in.vTex_0;
+    vTex[1] = in.vTex_1;
+    vTex[2] = in.vTex_2;
+    vTex[3] = in.vTex_3;
+    const uint gl_ViewIndex = spvViewMask[0];
+    out.FragColor = in.vColor * uTex.sample(uTexSmplr, vTex[int(gl_ViewIndex)]);
+    return out;
+}
+

reference/shaders-msl/vulkan/vert/multiview.multiview.no-layered.nocompat.vk.vert

@@ -0,0 +1,28 @@
+#include <metal_stdlib>
+#include <simd/simd.h>
+
+using namespace metal;
+
+struct MVPs
+{
+    float4x4 MVP[2];
+};
+
+struct main0_out
+{
+    float4 gl_Position [[position]];
+};
+
+struct main0_in
+{
+    float4 Position [[attribute(0)]];
+};
+
+vertex main0_out main0(main0_in in [[stage_in]], constant uint* spvViewMask [[buffer(24)]], constant MVPs& _19 [[buffer(0)]])
+{
+    main0_out out = {};
+    const uint gl_ViewIndex = spvViewMask[0];
+    out.gl_Position = _19.MVP[int(gl_ViewIndex)] * in.Position;
+    return out;
+}
+

shaders-msl/vulkan/frag/basic.multiview.no-layered.nocompat.vk.frag

@@ -0,0 +1,14 @@
+#version 310 es
+#extension GL_EXT_multiview : require
+precision mediump float;
+
+layout(location = 0) in vec4 vColor;
+layout(location = 1) in vec2 vTex[4];
+layout(binding = 0) uniform sampler2D uTex;
+layout(location = 0) out vec4 FragColor;
+
+void main()
+{
+    FragColor = vColor * texture(uTex, vTex[gl_ViewIndex]);
+}
+

shaders-msl/vulkan/vert/multiview.multiview.no-layered.nocompat.vk.vert

@@ -0,0 +1,14 @@
+#version 310 es
+#extension GL_EXT_multiview : require
+
+layout(std140, binding = 0) uniform MVPs
+{
+	mat4 MVP[2];
+};
+
+layout(location = 0) in vec4 Position;
+
+void main()
+{
+	gl_Position = MVP[gl_ViewIndex] * Position;
+}

spirv_cross_c.cpp

@@ -658,6 +658,10 @@ spvc_result spvc_compiler_options_set_uint(spvc_compiler_options options, spvc_c
 	case SPVC_COMPILER_OPTION_MSL_VERTEX_INDEX_TYPE:
 		options->msl.vertex_index_type = static_cast<CompilerMSL::Options::IndexType>(value);
 		break;
+
+	case SPVC_COMPILER_OPTION_MSL_MULTIVIEW_LAYERED_RENDERING:
+		options->msl.multiview_layered_rendering = value != 0;
+		break;
 #endif
 
 	default:

spirv_cross_c.h

@@ -33,7 +33,7 @@ extern "C" {
 /* Bumped if ABI or API breaks backwards compatibility. */
 #define SPVC_C_API_VERSION_MAJOR 0
 /* Bumped if APIs or enumerations are added in a backwards compatible way. */
-#define SPVC_C_API_VERSION_MINOR 37
+#define SPVC_C_API_VERSION_MINOR 38
 /* Bumped if internal implementation details change. */
 #define SPVC_C_API_VERSION_PATCH 0
 
@@ -636,6 +636,8 @@ typedef enum spvc_compiler_option
 
 	SPVC_COMPILER_OPTION_GLSL_FORCE_FLATTENED_IO_BLOCKS = 66 | SPVC_COMPILER_OPTION_GLSL_BIT,
 
+	SPVC_COMPILER_OPTION_MSL_MULTIVIEW_LAYERED_RENDERING = 67 | SPVC_COMPILER_OPTION_MSL_BIT,
+
 	SPVC_COMPILER_OPTION_INT_MAX = 0x7fffffff
 } spvc_compiler_option;
 

spirv_msl.cpp

@@ -146,6 +146,7 @@ void CompilerMSL::build_implicit_builtins()
 	bool need_subgroup_ge_mask = !msl_options.is_ios() && (active_input_builtins.get(BuiltInSubgroupGeMask) ||
 	                                                       active_input_builtins.get(BuiltInSubgroupGtMask));
 	bool need_multiview = get_execution_model() == ExecutionModelVertex && !msl_options.view_index_from_device_index &&
+	                      msl_options.multiview_layered_rendering &&
 	                      (msl_options.multiview || active_input_builtins.get(BuiltInViewIndex));
 	bool need_dispatch_base =
 	    msl_options.dispatch_base && get_execution_model() == ExecutionModelGLCompute &&
@@ -9242,7 +9243,7 @@ string CompilerMSL::member_attribute_qualifier(const SPIRType &type, uint32_t in
 			switch (builtin)
 			{
 			case BuiltInViewIndex:
-				if (!msl_options.multiview)
+				if (!msl_options.multiview || !msl_options.multiview_layered_rendering)
 					break;
 				/* fallthrough */
 			case BuiltInFrontFacing:
@@ -9660,7 +9661,8 @@ bool CompilerMSL::is_direct_input_builtin(BuiltIn bi_type)
 	case BuiltInBaryCoordNoPerspNV:
 		return false;
 	case BuiltInViewIndex:
-		return get_execution_model() == ExecutionModelFragment && msl_options.multiview;
+		return get_execution_model() == ExecutionModelFragment && msl_options.multiview &&
+		       msl_options.multiview_layered_rendering;
 	// Any stage function in
 	case BuiltInDeviceIndex:
 	case BuiltInSubgroupEqMask:
@@ -10430,6 +10432,15 @@ void CompilerMSL::fix_up_shader_inputs_outputs()
 					// Since every physical device is rendering a different view,
 					// there's no need for layered rendering here.
 				}
+				else if (!msl_options.multiview_layered_rendering)
+				{
+					// In this case, the views are rendered one at a time. The view index, then,
+					// is just the first part of the "view mask".
+					entry_func.fixup_hooks_in.push_back([=]() {
+						statement("const ", builtin_type_decl(bi_type), " ", to_expression(var_id), " = ",
+						          to_expression(view_mask_buffer_id), "[0];");
+					});
+				}
 				else if (get_execution_model() == ExecutionModelFragment)
 				{
 					// Because we adjusted the view index in the vertex shader, we have to

spirv_msl.hpp

@@ -290,6 +290,7 @@ class CompilerMSL : public CompilerGLSL
 		bool swizzle_texture_samples = false;
 		bool tess_domain_origin_lower_left = false;
 		bool multiview = false;
+		bool multiview_layered_rendering = true;
 		bool view_index_from_device_index = false;
 		bool dispatch_base = false;
 		bool texture_1D_as_2D = false;

test_shaders.py

@@ -232,6 +232,8 @@ def cross_compile_msl(shader, spirv, opt, iterations, paths):
         msl_args.append('--emit-line-directives')
     if '.multiview.' in shader:
         msl_args.append('--msl-multiview')
+    if '.no-layered.' in shader:
+        msl_args.append('--msl-multiview-no-layered-rendering')
     if '.viewfromdev.' in shader:
         msl_args.append('--msl-view-index-from-device-index')
     if '.dispatchbase.' in shader: