From e8b71b8dc5cd70535308591f1dd2dba5f92f44eb Mon Sep 17 00:00:00 2001
From: Dzmitry Malyshau <kvark@fastmail.com>
Date: Mon, 28 Jun 2021 12:38:11 -0400
Subject: [PATCH] [glsl-out] Support extended shadow sampling instructions, and
 the offset

---
 src/back/glsl/mod.rs                        | 49 +++++++++++++++++----
 tests/out/glsl/shadow.fs_main.Fragment.glsl |  2 +-
 2 files changed, 41 insertions(+), 10 deletions(-)

diff --git a/src/back/glsl/mod.rs b/src/back/glsl/mod.rs
index 2366fe81d6..877995b779 100644
--- a/src/back/glsl/mod.rs
+++ b/src/back/glsl/mod.rs
@@ -132,6 +132,9 @@ bitflags::bitflags! {
     pub struct WriterFlags: u32 {
         /// Extend output Z from (0,1) to (-1,1).
         const ADJUST_COORDINATE_SPACE = 0x1;
+        /// Supports GL_EXT_texture_shadow_lod on the host, which provides
+        /// additional functions on shadows and arrays of shadows.
+        const TEXTURE_SHADOW_LOD = 0x2;
     }
 }
 
@@ -391,6 +394,16 @@ impl<'a, W: Write> Writer<'a, W> {
         // preprocessor not the processor ¯\_(ツ)_/¯
         self.features.write(self.options.version, &mut self.out)?;
 
+        // Write the additional extensions
+        if self
+            .options
+            .writer_flags
+            .contains(WriterFlags::TEXTURE_SHADOW_LOD)
+        {
+            // https://www.khronos.org/registry/OpenGL/extensions/EXT/EXT_texture_shadow_lod.txt
+            writeln!(self.out, "#extension GL_EXT_texture_shadow_lod : require")?;
+        }
+
         // glsl es requires a precision to be specified for floats
         // TODO: Should this be user configurable?
         if es {
@@ -1677,19 +1690,27 @@ impl<'a, W: Write> Writer<'a, W> {
             // Furthermore if `depth_ref` is some we need to append it to the coordinate vector
             Expression::ImageSample {
                 image,
-                sampler: _, //TODO
+                sampler: _, //TODO?
                 coordinate,
                 array_index,
-                offset: _, //TODO
+                offset,
                 level,
                 depth_ref,
             } => {
-                //TODO: handle MS
+                let dim = match *ctx.info[image].ty.inner_with(&self.module.types) {
+                    TypeInner::Image { dim, .. } => dim,
+                    _ => unreachable!(),
+                };
 
                 // textureLod on sampler2DArrayShadow and samplerCubeShadow does not exist in GLSL.
                 // To emulate this, we will have to use textureGrad with a constant gradient of 0.
-                let workaround_lod_array_shadow_as_grad =
-                    array_index.is_some() && depth_ref.is_some();
+                let workaround_lod_array_shadow_as_grad = (array_index.is_some()
+                    || dim == crate::ImageDimension::Cube)
+                    && depth_ref.is_some()
+                    && !self
+                        .options
+                        .writer_flags
+                        .contains(WriterFlags::TEXTURE_SHADOW_LOD);
 
                 //Write the function to be used depending on the sample level
                 let fun_name = match level {
@@ -1703,8 +1724,12 @@ impl<'a, W: Write> Writer<'a, W> {
                     }
                     crate::SampleLevel::Gradient { .. } => "textureGrad",
                 };
+                let offset_name = match offset {
+                    Some(_) => "Offset",
+                    None => "",
+                };
 
-                write!(self.out, "{}(", fun_name)?;
+                write!(self.out, "{}{}(", fun_name, offset_name)?;
 
                 // Write the image that will be used
                 self.write_expr(image, ctx)?;
@@ -1745,15 +1770,16 @@ impl<'a, W: Write> Writer<'a, W> {
                     // Zero needs level set to 0
                     crate::SampleLevel::Zero => {
                         if workaround_lod_array_shadow_as_grad {
-                            write!(self.out, ", vec2(0, 0), vec2(0,0)")?;
+                            write!(self.out, ", vec2(0,0), vec2(0,0)")?;
                         } else {
-                            write!(self.out, ", 0")?;
+                            write!(self.out, ", 0.0")?;
                         }
                     }
                     // Exact and bias require another argument
                     crate::SampleLevel::Exact(expr) => {
                         if workaround_lod_array_shadow_as_grad {
-                            write!(self.out, ", vec2(0, 0), vec2(0,0)")?;
+                            log::warn!("Unable to `textureLod` a shadow array, ignoring the LOD");
+                            write!(self.out, ", vec2(0,0), vec2(0,0)")?;
                         } else {
                             write!(self.out, ", ")?;
                             self.write_expr(expr, ctx)?;
@@ -1771,6 +1797,11 @@ impl<'a, W: Write> Writer<'a, W> {
                     }
                 }
 
+                if let Some(constant) = offset {
+                    write!(self.out, ", ")?;
+                    self.write_constant(&self.module.constants[constant])?;
+                }
+
                 // End the function
                 write!(self.out, ")")?
             }
diff --git a/tests/out/glsl/shadow.fs_main.Fragment.glsl b/tests/out/glsl/shadow.fs_main.Fragment.glsl
index b49523b983..6446c56443 100644
--- a/tests/out/glsl/shadow.fs_main.Fragment.glsl
+++ b/tests/out/glsl/shadow.fs_main.Fragment.glsl
@@ -28,7 +28,7 @@ float fetch_shadow(uint light_id, vec4 homogeneous_coords) {
     }
     vec2 flip_correction = vec2(0.5, -0.5);
     vec2 light_local = (((homogeneous_coords.xy * flip_correction) / vec2(homogeneous_coords.w)) + vec2(0.5, 0.5));
-    float _expr26 = textureGrad(_group_0_binding_2, vec4(light_local, int(light_id), (homogeneous_coords.z / homogeneous_coords.w)), vec2(0, 0), vec2(0,0));
+    float _expr26 = textureGrad(_group_0_binding_2, vec4(light_local, int(light_id), (homogeneous_coords.z / homogeneous_coords.w)), vec2(0,0), vec2(0,0));
     return _expr26;
 }