metal: fix shader compilation when using void effect() with MRTs.

src/modules/graphics/Shader.cpp

@@ -26,6 +26,7 @@
 
 // glslang
 #include "libraries/glslang/glslang/Public/ShaderLang.h"
+#include "libraries/glslang/glslang/Public/ResourceLimits.h"
 
 // Needed for reflection information.
 #include "libraries/glslang/glslang/Include/Types.h"
@@ -1445,7 +1446,18 @@ void Shader::handleUnknownUniformName(const char */*name*/)
 
 bool Shader::initialize()
 {
-	return glslang::InitializeProcess();
+	bool success = glslang::InitializeProcess();
+	if (!success)
+		return false;
+
+	TBuiltInResource *resources = GetResources();
+	*resources = *GetDefaultResources();
+
+	// This is 32 in the default resource struct, which is too high for Metal.
+	// TODO: Set this based on what the system actually supports?
+	resources->maxDrawBuffers = 8;
+
+	return true;
 }
 
 void Shader::deinitialize()

src/modules/graphics/ShaderStage.cpp

@@ -62,7 +62,7 @@ ShaderStage::ShaderStage(Graphics *gfx, ShaderStageType stage, const std::string
 
 	bool forwardcompat = supportsGLSL3 && !forcedefault;
 
-	if (!glslangShader->parse(GetDefaultResources(), defaultversion, defaultprofile, forcedefault, forwardcompat, EShMsgSuppressWarnings))
+	if (!glslangShader->parse(GetResources(), defaultversion, defaultprofile, forcedefault, forwardcompat, EShMsgSuppressWarnings))
 	{
 		const char *stagename = "unknown";
 		getConstant(stage, stagename);

src/modules/graphics/metal/Shader.mm

@@ -208,7 +208,7 @@ Shader::Shader(id<MTLDevice> device, StrongRef<love::graphics::ShaderStage> stag
 		forcedefault = true;
 #endif
 
-		if (!tshader->parse(GetDefaultResources(), defaultversion, defaultprofile, forcedefault, forwardcompat, EShMsgSuppressWarnings))
+		if (!tshader->parse(GetResources(), defaultversion, defaultprofile, forcedefault, forwardcompat, EShMsgSuppressWarnings))
 		{
 			const char *stagename = "unknown";
 			ShaderStage::getConstant(stage, stagename);

src/modules/graphics/vulkan/Shader.cpp

@@ -554,7 +554,7 @@ void Shader::compileShaders()
 		bool forceDefault = false;
 		bool forwardCompat = true;
 
-		if (!tshader->parse(GetDefaultResources(), defaultVersion, defaultProfile, forceDefault, forwardCompat, EShMsgSuppressWarnings))
+		if (!tshader->parse(GetResources(), defaultVersion, defaultProfile, forceDefault, forwardCompat, EShMsgSuppressWarnings))
 		{
 			const char *stageName = "unknown";
 			ShaderStage::getConstant(stage, stageName);