brtshaderc integration fork - runtime shader compilation.

[matheusrsimon]

I've forked bgfx and integrated brtshaderc so it now can compile shaders at runtime in a limited number of platforms.

I did this, instead of patching brtshaderc itself because it required changes on shaderc.cpp and shaderc_spirv.cpp.

Usage:

static const char* s_basePath;

const char* joinPath(const char* first, const char* second);

bgfx::ProgramHandle createRuntimeShaderProgram(const char* vshName, const char* fshName, const char* varyingName)
{
	bgfx::RendererType::Enum rendererType = bgfx::getRendererType();
	const char* varyingPath = joinPath(s_basePath, varyingName);

	// compile vertex shader, with specific arguments for defines, varying def file, shader profile.
	const char* vshPath = joinPath(s_basePath, vshName);
	const char* vshProfile = shaderc::getProfile(rendererType, shaderc::ST_VERTEX);
	const bgfx::Memory* vshMemory =  shaderc::compileShader(shaderc::ST_VERTEX, vshPath, NULL, varyingPath, vshProfile);
	bgfx::ShaderHandle vsh = bgfx::createShader(vshMemory);

	// compile fragment shader, with specific arguments for defines, varying def file, shader profile.
	const char* fshPath = joinPath(s_basePath, fshName);
	const char* fshProfile = shaderc::getProfile(rendererType, shaderc::ST_FRAGMENT);
	const bgfx::Memory* fshMemory =  shaderc::compileShader(shaderc::ST_FRAGMENT, fshPath, NULL, varyingPath, fshProfile);
	bgfx::ShaderHandle fsh = bgfx::createShader(fshMemory);

	return bgfx::createProgram(vsh, fsh, true);
}