Fix shadow flickering with async shader compilation

This mostly reverts the approach in #62628, which now the problem is better scoped, looks overengineered and instead focuses on the few cases where there's something to take care of.

(cherry picked from commit a2ed82d3b20d931f872e2edc7ddd672544ed7947)

drivers/gles3/rasterizer_scene_gles3.cpp

@@ -4111,6 +4111,13 @@ void RasterizerSceneGLES3::render_scene(const Transform &p_cam_transform, const
 		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_COMPARE_FUNC, GL_LESS);
 		state.ubo_data.shadow_atlas_pixel_size[0] = 1.0 / shadow_atlas->size;
 		state.ubo_data.shadow_atlas_pixel_size[1] = 1.0 / shadow_atlas->size;
+	} else {
+		if (storage->config.async_compilation_enabled) {
+			// Avoid GL UB message id 131222 caused by shadow samplers not properly set up in the ubershader
+			glActiveTexture(GL_TEXTURE0 + storage->config.max_texture_image_units - 6);
+			glBindTexture(GL_TEXTURE_2D, storage->resources.depth_tex);
+			glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_COMPARE_MODE, GL_COMPARE_REF_TO_TEXTURE);
+		}
 	}
 
 	if (reflection_atlas && reflection_atlas->size) {
@@ -4866,6 +4873,13 @@ void RasterizerSceneGLES3::render_shadow(RID p_light, RID p_shadow_atlas, int p_
 	state.ubo_data.shadow_dual_paraboloid_render_zfar = zfar;
 	state.ubo_data.opaque_prepass_threshold = 0.1;
 
+	if (storage->config.async_compilation_enabled) {
+		// Avoid GL UB message id 131222 caused by shadow samplers not properly set up in the ubershader
+		glActiveTexture(GL_TEXTURE0 + storage->config.max_texture_image_units - 6);
+		glBindTexture(GL_TEXTURE_2D, storage->resources.depth_tex);
+		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_COMPARE_MODE, GL_COMPARE_REF_TO_TEXTURE);
+	}
+
 	_setup_environment(nullptr, light_projection, light_transform);
 
 	state.scene_shader.set_conditional(SceneShaderGLES3::RENDER_DEPTH, true);
@@ -5297,7 +5311,7 @@ void RasterizerSceneGLES3::initialize() {
 	glFrontFace(GL_CW);
 
 	if (storage->config.async_compilation_enabled) {
-		state.scene_shader.init_async_compilation(storage->resources.depth_tex);
+		state.scene_shader.init_async_compilation();
 	}
 }
 

drivers/gles3/rasterizer_storage_gles3.cpp

@@ -8354,7 +8354,7 @@ void RasterizerStorageGLES3::initialize() {
 	shaders.cubemap_filter.set_conditional(CubemapFilterShaderGLES3::LOW_QUALITY, !ggx_hq);
 	shaders.particles.init();
 	if (config.async_compilation_enabled) {
-		shaders.particles.init_async_compilation(resources.depth_tex);
+		shaders.particles.init_async_compilation();
 	}
 
 #ifdef GLES_OVER_GL

drivers/gles3/shader_gles3.cpp

@@ -177,45 +177,29 @@ bool ShaderGLES3::is_custom_code_ready_for_render(uint32_t p_code_id) {
 	return true;
 }
 
-bool ShaderGLES3::_bind_ubershader() {
+bool ShaderGLES3::_bind_ubershader(bool p_for_warmup) {
 #ifdef DEBUG_ENABLED
 	ERR_FAIL_COND_V(!is_async_compilation_supported(), false);
 	ERR_FAIL_COND_V(get_ubershader_flags_uniform() == -1, false);
 #endif
 	new_conditional_version.version |= VersionKey::UBERSHADER_FLAG;
 	bool bound = _bind(true);
+	new_conditional_version.version &= ~VersionKey::UBERSHADER_FLAG;
+	if (p_for_warmup) {
+		// Avoid GL UB message id 131222 caused by shadow samplers not properly set up yet
+		unbind();
+		return bound;
+	}
 	int conditionals_uniform = _get_uniform(get_ubershader_flags_uniform());
 #ifdef DEBUG_ENABLED
 	ERR_FAIL_COND_V(conditionals_uniform == -1, false);
 #endif
-	new_conditional_version.version &= ~VersionKey::UBERSHADER_FLAG;
 #ifdef DEV_ENABLED
 	// So far we don't need bit 31 for conditionals. That allows us to use signed integers,
 	// which are more compatible across GL driver vendors.
 	CRASH_COND(new_conditional_version.version >= 0x80000000);
 #endif
 	glUniform1i(conditionals_uniform, new_conditional_version.version);
-
-	// This is done to avoid running into the GL UB message id 131222. Long explanation:
-	// If an ubershader has shadow samplers, they are generally not used if the current material has shadowing disabled,
-	// but that also implies the rasterizer won't do any preparation to the relevant shadow samplers (which won't really exist,
-	// so that's the correct way in a conditioned shader).
-	// However, in the case of the ubershader those shadow samplers are unconditionally declared, although potentially unused and
-	// thus "uninitialized". Sampling in that situation (compare disabled, no depth texture bound) is undefined behavior for GL.
-	// And that's a problem for us because, even if dynamic branching will serve to avoid using the unprepared sampler when shadowing
-	// is not enabled, the GPU may still run the other branch. And it's not just that the results from the sampling are undefined
-	// (that wouldn't be a problem and we could just ignore the warning); the problem is that sampling in that state is fully UB.
-	for (int i = 0; i < shadow_texunit_count; i++) {
-		int unit = shadow_texunits[i];
-		if (unit >= 0) {
-			glActiveTexture(GL_TEXTURE0 + unit);
-		} else {
-			glActiveTexture(GL_TEXTURE0 + max_image_units + unit);
-		}
-		glBindTexture(GL_TEXTURE_2D, depth_tex);
-		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_COMPARE_MODE, GL_COMPARE_REF_TO_TEXTURE);
-	}
-
 	return bound;
 }
 
@@ -1128,7 +1112,7 @@ GLint ShaderGLES3::get_uniform_location(const String &p_name) const {
 	return glGetUniformLocation(version->ids.main, p_name.ascii().get_data());
 }
 
-void ShaderGLES3::setup(const char **p_conditional_defines, int p_conditional_count, const char **p_uniform_names, int p_uniform_count, const AttributePair *p_attribute_pairs, int p_attribute_count, const TexUnitPair *p_texunit_pairs, int p_texunit_pair_count, const int *p_shadow_texunits, int p_shadow_texunit_count, const UBOPair *p_ubo_pairs, int p_ubo_pair_count, const Feedback *p_feedback, int p_feedback_count, const char *p_vertex_code, const char *p_fragment_code, int p_vertex_code_start, int p_fragment_code_start) {
+void ShaderGLES3::setup(const char **p_conditional_defines, int p_conditional_count, const char **p_uniform_names, int p_uniform_count, const AttributePair *p_attribute_pairs, int p_attribute_count, const TexUnitPair *p_texunit_pairs, int p_texunit_pair_count, const UBOPair *p_ubo_pairs, int p_ubo_pair_count, const Feedback *p_feedback, int p_feedback_count, const char *p_vertex_code, const char *p_fragment_code, int p_vertex_code_start, int p_fragment_code_start) {
 	ERR_FAIL_COND(version);
 	conditional_version.key = 0;
 	new_conditional_version.key = 0;
@@ -1140,8 +1124,6 @@ void ShaderGLES3::setup(const char **p_conditional_defines, int p_conditional_co
 	fragment_code = p_fragment_code;
 	texunit_pairs = p_texunit_pairs;
 	texunit_pair_count = p_texunit_pair_count;
-	shadow_texunits = p_shadow_texunits;
-	shadow_texunit_count = p_shadow_texunit_count;
 	vertex_code_start = p_vertex_code_start;
 	fragment_code_start = p_fragment_code_start;
 	attribute_pairs = p_attribute_pairs;
@@ -1232,12 +1214,11 @@ void ShaderGLES3::setup(const char **p_conditional_defines, int p_conditional_co
 	glGetIntegerv(GL_MAX_TEXTURE_IMAGE_UNITS, &max_image_units);
 }
 
-void ShaderGLES3::init_async_compilation(GLuint p_depth_tex) {
-	depth_tex = p_depth_tex;
+void ShaderGLES3::init_async_compilation() {
 	if (is_async_compilation_supported() && get_ubershader_flags_uniform() != -1) {
 		// Warm up the ubershader for the case of no custom code
 		new_conditional_version.code_version = 0;
-		_bind_ubershader();
+		_bind_ubershader(true);
 	}
 }
 
@@ -1297,7 +1278,7 @@ void ShaderGLES3::set_custom_shader_code(uint32_t p_code_id, const String &p_ver
 	if (p_async_mode == ASYNC_MODE_VISIBLE && is_async_compilation_supported() && get_ubershader_flags_uniform() != -1) {
 		// Warm up the ubershader for this custom code
 		new_conditional_version.code_version = p_code_id;
-		_bind_ubershader();
+		_bind_ubershader(true);
 	}
 }
 

drivers/gles3/shader_gles3.h

@@ -96,7 +96,6 @@ private:
 	//@TODO Optimize to a fixed set of shader pools and use a LRU
 	int uniform_count;
 	int texunit_pair_count;
-	int shadow_texunit_count;
 	int conditional_count;
 	int ubo_count;
 	int feedback_count;
@@ -246,7 +245,6 @@ private:
 	const char **uniform_names;
 	const AttributePair *attribute_pairs;
 	const TexUnitPair *texunit_pairs;
-	const int *shadow_texunits;
 	const UBOPair *ubo_pairs;
 	const Feedback *feedbacks;
 	const char *vertex_code;
@@ -280,7 +278,6 @@ private:
 	static ShaderGLES3 *active;
 
 	int max_image_units;
-	GLuint depth_tex = 0;
 
 	_FORCE_INLINE_ void _set_uniform_variant(GLint p_uniform, const Variant &p_value) {
 		if (p_uniform < 0) {
@@ -372,13 +369,13 @@ private:
 	}
 
 	bool _bind(bool p_binding_fallback);
-	bool _bind_ubershader();
+	bool _bind_ubershader(bool p_for_warmrup = false);
 
 protected:
 	_FORCE_INLINE_ int _get_uniform(int p_which) const;
 	_FORCE_INLINE_ void _set_conditional(int p_which, bool p_value);
 
-	void setup(const char **p_conditional_defines, int p_conditional_count, const char **p_uniform_names, int p_uniform_count, const AttributePair *p_attribute_pairs, int p_attribute_count, const TexUnitPair *p_texunit_pairs, int p_texunit_pair_count, const int *p_shadow_texunits, int p_shadow_texunit_count, const UBOPair *p_ubo_pairs, int p_ubo_pair_count, const Feedback *p_feedback, int p_feedback_count, const char *p_vertex_code, const char *p_fragment_code, int p_vertex_code_start, int p_fragment_code_start);
+	void setup(const char **p_conditional_defines, int p_conditional_count, const char **p_uniform_names, int p_uniform_count, const AttributePair *p_attribute_pairs, int p_attribute_count, const TexUnitPair *p_texunit_pairs, int p_texunit_pair_count, const UBOPair *p_ubo_pairs, int p_ubo_pair_count, const Feedback *p_feedback, int p_feedback_count, const char *p_vertex_code, const char *p_fragment_code, int p_vertex_code_start, int p_fragment_code_start);
 
 	ShaderGLES3();
 
@@ -407,7 +404,7 @@ public:
 	_FORCE_INLINE_ bool is_version_valid() const { return version && version->compile_status == Version::COMPILE_STATUS_OK; }
 
 	virtual void init() = 0;
-	void init_async_compilation(GLuint p_depth_tex);
+	void init_async_compilation();
 	bool is_async_compilation_supported();
 	void finish();
 

gles_builders.py

@@ -19,7 +19,6 @@ class LegacyGLHeaderStruct:
         self.enums = {}
         self.texunits = []
         self.texunit_names = []
-        self.shadow_texunits = []
         self.ubos = []
         self.ubo_names = []
 
@@ -107,8 +106,6 @@ def include_file_in_legacygl_header(filename, header_data, depth):
 
                 if not x in header_data.texunit_names:
                     header_data.texunits += [(x, texunit)]
-                    if line.find("sampler2DShadow") != -1:
-                        header_data.shadow_texunits += [texunit]
                     header_data.texunit_names += [x]
 
         elif line.find("uniform") != -1 and line.lower().find("ubo:") != -1:
@@ -486,15 +483,6 @@ def build_legacygl_header(filename, include, class_suffix, output_attribs, gles2
     else:
         fd.write("\t\tstatic TexUnitPair *_texunit_pairs=NULL;\n")
 
-    if not gles2:
-        if header_data.shadow_texunits:
-            fd.write("\t\tstatic int _shadow_texunits[]={")
-            for x in header_data.shadow_texunits:
-                fd.write(str(x) + ',')
-            fd.write("};\n\n")
-        else:
-            fd.write("\t\tstatic int *_shadow_texunits=NULL;\n")
-
     if not gles2 and header_data.ubos:
         fd.write("\t\tstatic UBOPair _ubo_pairs[]={\n")
         for x in header_data.ubos:
@@ -549,8 +537,6 @@ def build_legacygl_header(filename, include, class_suffix, output_attribs, gles2
                 + str(len(header_data.attributes))
                 + ", _texunit_pairs,"
                 + str(len(header_data.texunits))
-                + ", _shadow_texunits,"
-                + str(len(header_data.shadow_texunits))
                 + ",_ubo_pairs,"
                 + str(len(header_data.ubos))
                 + ",_feedbacks,"
@@ -580,8 +566,6 @@ def build_legacygl_header(filename, include, class_suffix, output_attribs, gles2
                 + str(len(header_data.uniforms))
                 + ",_texunit_pairs,"
                 + str(len(header_data.texunits))
-                + ",_shadow_texunits,"
-                + str(len(header_data.shadow_texunits))
                 + ",_enums,"
                 + str(len(header_data.enums))
                 + ",_enum_values,"