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[glsl-out] Document and flatten back::glsl::Writer::write_varying.
This commit is contained in:
Jim Blandy
@@ -1116,94 +1116,126 @@ impl<'a, W: Write> Writer<'a, W> {
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Ok(())
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}
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/// Writes the varying declaration.
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/// Write a GLSL global that will carry a Naga entry point's argument or return value.
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///
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/// A Naga entry point's arguments and return value are rendered in GLSL as
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/// variables at global scope with the `in` and `out` storage qualifiers.
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/// The code we generate for `main` loads from all the `in` globals into
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/// appropriately named locals. Before it returns, `main` assigns the
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/// components of its return value into all the `out` globals.
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///
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/// This function writes a declaration for one such GLSL global,
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/// representing a value passed into or returned from [`self.entry_point`]
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/// that has a [`Location`] binding. The global's name is generated based on
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/// the location index and the shader stages being connected; see
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/// [`VaryingName`]. This means we don't need to know the names of
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/// arguments, just their types and bindings.
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///
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/// Emit nothing for entry point arguments or return values with [`BuiltIn`]
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/// bindings; `main` will read from or assign to the appropriate GLSL
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/// special variable; these are pre-declared. As an exception, we do declare
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/// `gl_Position` or `gl_FragCoord` with the `invariant` qualifier if
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/// needed.
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///
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/// Use `output` together with [`self.entry_point.stage`] to determine which
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/// shader stages are being connected, and choose the `in` or `out` storage
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/// qualifier.
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///
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/// [`self.entry_point`]: Writer::entry_point
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/// [`self.entry_point.stage`]: crate::EntryPoint::stage
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/// [`Location`]: crate::Binding::Location
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/// [`BuiltIn`]: crate::Binding::BuiltIn
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fn write_varying(
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&mut self,
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binding: Option<&crate::Binding>,
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ty: Handle<crate::Type>,
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output: bool,
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) -> Result<(), Error> {
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match self.module.types[ty].inner {
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crate::TypeInner::Struct { ref members, .. } => {
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for member in members {
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self.write_varying(member.binding.as_ref(), member.ty, output)?;
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}
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// For a struct, emit a separate global for each member with a binding.
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if let crate::TypeInner::Struct { ref members, .. } = self.module.types[ty].inner {
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for member in members {
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self.write_varying(member.binding.as_ref(), member.ty, output)?;
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}
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_ => {
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let (location, interpolation, sampling) = match binding {
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Some(&crate::Binding::Location {
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location,
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interpolation,
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sampling,
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}) => (location, interpolation, sampling),
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Some(&crate::Binding::BuiltIn {
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built_in,
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invariant: true,
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}) => {
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writeln!(self.out, "invariant {};", glsl_built_in(built_in, output))?;
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return Ok(());
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}
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_ => return Ok(()),
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};
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return Ok(());
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}
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// Write the interpolation modifier if needed
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//
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// We ignore all interpolation and auxiliary modifiers that aren't used in fragment
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// shaders' input globals or vertex shaders' output globals.
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let emit_interpolation_and_auxiliary = match self.entry_point.stage {
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ShaderStage::Vertex => output,
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ShaderStage::Fragment => !output,
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_ => false,
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};
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let binding = match binding {
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None => return Ok(()),
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Some(binding) => binding,
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};
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// Write the I/O locations, if allowed
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if self.options.version.supports_explicit_locations()
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|| !emit_interpolation_and_auxiliary
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{
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write!(self.out, "layout(location = {}) ", location)?;
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let (location, interpolation, sampling) = match *binding {
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crate::Binding::Location {
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location,
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interpolation,
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sampling,
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} => (location, interpolation, sampling),
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crate::Binding::BuiltIn {
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built_in,
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invariant,
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} => {
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if invariant {
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writeln!(self.out, "invariant {};", glsl_built_in(built_in, output))?;
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}
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return Ok(());
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}
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};
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// Write the interpolation qualifier.
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if let Some(interp) = interpolation {
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if emit_interpolation_and_auxiliary {
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write!(self.out, "{} ", glsl_interpolation(interp))?;
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}
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}
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// Write the interpolation modifier if needed
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//
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// We ignore all interpolation and auxiliary modifiers that aren't used in fragment
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// shaders' input globals or vertex shaders' output globals.
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let emit_interpolation_and_auxiliary = match self.entry_point.stage {
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ShaderStage::Vertex => output,
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ShaderStage::Fragment => !output,
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_ => false,
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};
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// Write the sampling auxiliary qualifier.
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//
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// Before GLSL 4.2, the `centroid` and `sample` qualifiers were required to appear
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// immediately before the `in` / `out` qualifier, so we'll just follow that rule
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// here, regardless of the version.
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if let Some(sampling) = sampling {
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if emit_interpolation_and_auxiliary {
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if let Some(qualifier) = glsl_sampling(sampling) {
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write!(self.out, "{} ", qualifier)?;
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}
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}
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}
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// Write the I/O locations, if allowed
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if self.options.version.supports_explicit_locations() || !emit_interpolation_and_auxiliary {
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write!(self.out, "layout(location = {}) ", location)?;
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}
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// Write the input/output qualifier.
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write!(self.out, "{} ", if output { "out" } else { "in" })?;
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// Write the type
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// `write_type` adds no leading or trailing spaces
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self.write_type(ty)?;
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// Finally write the global name and end the global with a `;` and a newline
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// Leading space is important
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let vname = VaryingName {
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binding: &crate::Binding::Location {
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location,
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interpolation: None,
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sampling: None,
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},
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stage: self.entry_point.stage,
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output,
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};
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writeln!(self.out, " {};", vname)?;
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// Write the interpolation qualifier.
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if let Some(interp) = interpolation {
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if emit_interpolation_and_auxiliary {
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write!(self.out, "{} ", glsl_interpolation(interp))?;
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}
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}
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// Write the sampling auxiliary qualifier.
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//
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// Before GLSL 4.2, the `centroid` and `sample` qualifiers were required to appear
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// immediately before the `in` / `out` qualifier, so we'll just follow that rule
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// here, regardless of the version.
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if let Some(sampling) = sampling {
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if emit_interpolation_and_auxiliary {
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if let Some(qualifier) = glsl_sampling(sampling) {
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write!(self.out, "{} ", qualifier)?;
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}
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}
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}
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// Write the input/output qualifier.
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write!(self.out, "{} ", if output { "out" } else { "in" })?;
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// Write the type
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// `write_type` adds no leading or trailing spaces
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self.write_type(ty)?;
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// Finally write the global name and end the global with a `;` and a newline
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// Leading space is important
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let vname = VaryingName {
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binding: &crate::Binding::Location {
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location,
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interpolation: None,
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sampling: None,
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},
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stage: self.entry_point.stage,
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output,
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};
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writeln!(self.out, " {};", vname)?;
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Ok(())
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}
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