[Fix] (DirectGLES): report distinct depth/stencil framebuffers as unsupported

GL only requires framebuffers whose depth and stencil attachments refer to the
same image; anything else may be answered GL_FRAMEBUFFER_UNSUPPORTED, and both
backends' real targets do exactly that - DirectVulkan cannot form two separate
attachments at all, and the ES drivers behind DirectGLES return UNSUPPORTED for
a separate depth renderbuffer plus stencil renderbuffer.

The frontend already knew how to detect the configuration, but only consulted it
for DirectVulkan. On DirectGLES it answered GL_FRAMEBUFFER_COMPLETE for a
framebuffer the driver had rejected, so every clear and draw against it was
silently dropped and the results read back as zeros - which is what
KHR-GL3x.packed_depth_stencil.verify_mixed_attachments saw. (That test
explicitly tolerates GL_FRAMEBUFFER_UNSUPPORTED; what it cannot survive is being
told the framebuffer works.)

Turned into a backend capability rather than a backend-type check, probed once
at init from a scratch framebuffer the same way the format-capability cache is,
so a driver that does support the configuration keeps using it. Defaults to
supported, leaving any backend that does not set it on the permissive path.

Fixes KHR-GL3{2,3}.packed_depth_stencil.verify_mixed_attachments for both
formats; DirectVulkan re-verified unchanged at 23/25 pass + 2 not-supported.

MobileGL/MG_Backend/BackendObject.h

@@ -324,6 +324,13 @@ namespace MobileGL {
             Float MaxFragmentInterpolationOffset = 0.4375f;
             Int FragmentInterpolationOffsetBits = 4;
             Bool SupportsWideLines = false;
+            // Whether a framebuffer whose depth and stencil attachments are distinct
+            // images can be rendered to. GL only requires support when both refer to the
+            // same image and lets an implementation answer GL_FRAMEBUFFER_UNSUPPORTED
+            // otherwise, which is what DirectVulkan (one combined attachment) and the
+            // real ES drivers behind DirectGLES both do. Defaults to true so a backend
+            // that never sets it keeps the permissive behaviour.
+            Bool SupportsDistinctDepthStencilAttachments = true;
             SizeT MaxShaderStorageBlockSize = 128 * 1024 * 1024;
             Uint32 SubgroupSize = 0;
             Uint32 SubgroupSupportedStages = 0;

MobileGL/MG_Backend/DirectGLES/BackendObject_DirectGLES.cpp

@@ -357,6 +357,42 @@ namespace MobileGL::MG_Backend::DirectGLES {
             return complete;
         }
 
+        // Whether the driver renders to a framebuffer whose depth and stencil come from
+        // two different renderbuffers. GL only requires support when both attachments are
+        // the same image, and ES drivers commonly answer GL_FRAMEBUFFER_UNSUPPORTED here;
+        // reporting COMPLETE from the frontend and then rendering into a framebuffer the
+        // driver refuses leaves the results silently empty.
+        Bool ProbeDistinctDepthStencilAttachments(const MG_External::GLESFunctionsTable& gl) {
+            if (!gl.glGenFramebuffers || !gl.glBindFramebuffer || !gl.glFramebufferRenderbuffer ||
+                !gl.glCheckFramebufferStatus || !gl.glDeleteFramebuffers || !gl.glGenRenderbuffers ||
+                !gl.glBindRenderbuffer || !gl.glRenderbufferStorage || !gl.glDeleteRenderbuffers) {
+                return true;
+            }
+
+            GLint prevFramebuffer = 0, prevRenderbuffer = 0;
+            gl.glGetIntegerv(GL_FRAMEBUFFER_BINDING, &prevFramebuffer);
+            gl.glGetIntegerv(GL_RENDERBUFFER_BINDING, &prevRenderbuffer);
+
+            GLuint framebuffer = 0;
+            GLuint renderbuffers[2] = {0, 0};
+            gl.glGenFramebuffers(1, &framebuffer);
+            gl.glGenRenderbuffers(2, renderbuffers);
+            gl.glBindRenderbuffer(GL_RENDERBUFFER, renderbuffers[0]);
+            gl.glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT16, 4, 4);
+            gl.glBindRenderbuffer(GL_RENDERBUFFER, renderbuffers[1]);
+            gl.glRenderbufferStorage(GL_RENDERBUFFER, GL_STENCIL_INDEX8, 4, 4);
+            gl.glBindFramebuffer(GL_FRAMEBUFFER, framebuffer);
+            gl.glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, renderbuffers[0]);
+            gl.glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_STENCIL_ATTACHMENT, GL_RENDERBUFFER, renderbuffers[1]);
+            const Bool supported = gl.glCheckFramebufferStatus(GL_FRAMEBUFFER) == GL_FRAMEBUFFER_COMPLETE;
+
+            gl.glBindFramebuffer(GL_FRAMEBUFFER, static_cast<GLuint>(prevFramebuffer));
+            gl.glBindRenderbuffer(GL_RENDERBUFFER, static_cast<GLuint>(prevRenderbuffer));
+            gl.glDeleteFramebuffers(1, &framebuffer);
+            gl.glDeleteRenderbuffers(2, renderbuffers);
+            return supported;
+        }
+
         Bool ProbeFramebufferCompletenessForRenderbuffer(const MG_External::GLESFunctionsTable& gl,
                                                         GLuint renderbuffer,
                                                         TextureInternalFormat format) {
@@ -1046,6 +1082,8 @@ namespace MobileGL::MG_Backend::DirectGLES {
             clampStageImageUniforms(m_GLESCapabilities.MaxFragmentImageUniforms);
         m_dynamicParameters.MaxComputeImageUniforms =
             clampStageImageUniforms(m_GLESCapabilities.MaxComputeImageUniforms);
+        m_dynamicParameters.SupportsDistinctDepthStencilAttachments =
+            ProbeDistinctDepthStencilAttachments(DirectGLES::g_GLESFuncs);
         m_dynamicParameters.MaxDrawBuffers = m_GLESCapabilities.MaxDrawBuffers;
         m_dynamicParameters.MaxColorAttachments = m_GLESCapabilities.MaxColorAttachments;
         m_dynamicParameters.MaxClipDistances = m_GLESCapabilities.MaxClipDistances;

MobileGL/MG_Impl/GLImpl/Framebuffer/GL_Framebuffer.cpp

@@ -22,9 +22,21 @@
 
 namespace MobileGL::MG_Impl::GLImpl {
     namespace {
-        Bool IsActiveBackendDirectVulkan() {
+        // GL only requires support for framebuffers whose depth and stencil attachments
+        // are the same image; anything else may be reported GL_FRAMEBUFFER_UNSUPPORTED.
+        // DirectVulkan cannot form two separate attachments at all, and the real ES
+        // drivers behind DirectGLES answer UNSUPPORTED for it too - so saying COMPLETE
+        // and then rendering into a framebuffer the driver refuses produced silently
+        // empty results (KHR-GL3x.packed_depth_stencil.verify_mixed_attachments).
+        Bool ActiveBackendRejectsDistinctDepthStencil() {
             auto* activeBackend = MG_Backend::pActiveBackendObject.get();
-            return activeBackend != nullptr && activeBackend->GetBackendType() == BackendType::DirectVulkan;
+            if (activeBackend == nullptr) {
+                return false;
+            }
+            if (activeBackend->GetBackendType() == BackendType::DirectVulkan) {
+                return true;
+            }
+            return !activeBackend->GetDynamicParameters().SupportsDistinctDepthStencilAttachments;
         }
 
         Bool HasDistinctCompleteDepthStencilTextureAttachments(
@@ -66,7 +78,7 @@ namespace MobileGL::MG_Impl::GLImpl {
                    (depthAttachment.IsTexture() || stencilAttachment.IsTexture());
         }
 
-        Bool IsUnsupportedFramebufferForDirectVulkan(
+        Bool HasUnsupportedDistinctDepthStencilAttachments(
             const MG_State::GLState::FramebufferObject& framebufferObject) {
             // TODO: Keep this in sync with DirectVulkan renderbuffer support as color renderbuffer rendering lands.
             return HasDistinctCompleteDepthStencilTextureAttachments(framebufferObject) ||
@@ -1631,8 +1643,8 @@ namespace MobileGL::MG_Impl::GLImpl {
         if (HasNonRenderableColorAttachment(*framebufferObject)) {
             return GL_FRAMEBUFFER_UNSUPPORTED;
         }
-        if (IsActiveBackendDirectVulkan() &&
+        if (ActiveBackendRejectsDistinctDepthStencil() &&
-            IsUnsupportedFramebufferForDirectVulkan(*framebufferObject)) {
+            HasUnsupportedDistinctDepthStencilAttachments(*framebufferObject)) {
             return GL_FRAMEBUFFER_UNSUPPORTED;
         }
         return GL_FRAMEBUFFER_COMPLETE;
@@ -1659,8 +1671,8 @@ namespace MobileGL::MG_Impl::GLImpl {
         if (HasNonRenderableColorAttachment(*framebufferObject)) {
             return GL_FRAMEBUFFER_UNSUPPORTED;
         }
-        if (IsActiveBackendDirectVulkan() &&
+        if (ActiveBackendRejectsDistinctDepthStencil() &&
-            IsUnsupportedFramebufferForDirectVulkan(*framebufferObject)) {
+            HasUnsupportedDistinctDepthStencilAttachments(*framebufferObject)) {
             return GL_FRAMEBUFFER_UNSUPPORTED;
         }
         return GL_FRAMEBUFFER_COMPLETE;