From 38d304f2fe187e4a748cc811b9b4569e15d5b606 Mon Sep 17 00:00:00 2001
From: rdb <git@rdb.name>
Date: Sun, 17 Jan 2021 12:10:42 +0100
Subject: [PATCH] glgsg: Force nearest filtering on isampler/usampler

Without this, Intel drivers will sample (0, 0, 0, 1)
---
 .../glstuff/glGraphicsStateGuardian_src.cxx   | 18 ++++++++++++++----
 panda/src/glstuff/glShaderContext_src.cxx     |  5 +++++
 panda/src/gobj/texture.cxx                    | 19 +++++++++++++++++++
 panda/src/gobj/texture.h                      |  1 +
 4 files changed, 39 insertions(+), 4 deletions(-)

diff --git a/panda/src/glstuff/glGraphicsStateGuardian_src.cxx b/panda/src/glstuff/glGraphicsStateGuardian_src.cxx
index bb2dfdc6fb..38f6ccb24f 100644
--- a/panda/src/glstuff/glGraphicsStateGuardian_src.cxx
+++ b/panda/src/glstuff/glGraphicsStateGuardian_src.cxx
@@ -12409,10 +12409,20 @@ specify_texture(CLP(TextureContext) *gtc, const SamplerState &sampler) {
     }
   }
 
-  glTexParameteri(target, GL_TEXTURE_MIN_FILTER,
-                  get_texture_filter_type(minfilter, !uses_mipmaps));
-  glTexParameteri(target, GL_TEXTURE_MAG_FILTER,
-                  get_texture_filter_type(magfilter, true));
+  if (Texture::is_integer(tex->get_format())) {
+    // Integer format textures can't have filtering enabled, and in fact, some
+    // drivers (looking at you, Intel) will always sample (0, 0, 0, 1) if we
+    // don't set this correctly!
+    glTexParameteri(target, GL_TEXTURE_MIN_FILTER,
+                    uses_mipmaps ? GL_NEAREST_MIPMAP_NEAREST
+                                 : GL_NEAREST);
+    glTexParameteri(target, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
+  } else {
+    glTexParameteri(target, GL_TEXTURE_MIN_FILTER,
+                    get_texture_filter_type(minfilter, !uses_mipmaps));
+    glTexParameteri(target, GL_TEXTURE_MAG_FILTER,
+                    get_texture_filter_type(magfilter, true));
+  }
 
   // Set anisotropic filtering.
   if (_supports_anisotropy) {
diff --git a/panda/src/glstuff/glShaderContext_src.cxx b/panda/src/glstuff/glShaderContext_src.cxx
index b0dfd4531b..424cf2ca83 100644
--- a/panda/src/glstuff/glShaderContext_src.cxx
+++ b/panda/src/glstuff/glShaderContext_src.cxx
@@ -2849,6 +2849,11 @@ update_shader_texture_bindings(ShaderContext *prev) {
       }
       continue;
     }
+    else if (Texture::is_integer(tex->get_format())) {
+      // Required to satisfy Intel drivers, which will otherwise sample zero.
+      sampler.set_minfilter(sampler.uses_mipmaps() ? SamplerState::FT_nearest_mipmap_nearest : SamplerState::FT_nearest);
+      sampler.set_magfilter(SamplerState::FT_nearest);
+    }
 
     if (tex->get_texture_type() != spec._desired_type) {
       switch (spec._part) {
diff --git a/panda/src/gobj/texture.cxx b/panda/src/gobj/texture.cxx
index d1d76d471c..a5658c8146 100644
--- a/panda/src/gobj/texture.cxx
+++ b/panda/src/gobj/texture.cxx
@@ -2628,6 +2628,25 @@ is_srgb(Format format) {
   }
 }
 
+/**
+ * Returns true if the indicated format is an integer format, false otherwise.
+ */
+bool Texture::
+is_integer(Format format) {
+  switch (format) {
+  case F_r32i:
+  case F_r8i:
+  case F_rg8i:
+  case F_rgb8i:
+  case F_rgba8i:
+  case F_r16i:
+    return true;
+
+  default:
+    return false;
+  }
+}
+
 /**
  * Computes the proper size of the texture, based on the original size, the
  * filename, and the resizing whims of the config file.
diff --git a/panda/src/gobj/texture.h b/panda/src/gobj/texture.h
index 7cb5f305fb..af96f49d1d 100644
--- a/panda/src/gobj/texture.h
+++ b/panda/src/gobj/texture.h
@@ -625,6 +625,7 @@ public:
   static bool has_alpha(Format format);
   static bool has_binary_alpha(Format format);
   static bool is_srgb(Format format);
+  static bool is_integer(Format format);
 
   static bool adjust_size(int &x_size, int &y_size, const std::string &name,
                           bool for_padding, AutoTextureScale auto_texture_scale = ATS_unspecified);