gex-gl host: framebuffer and renderbuffer names generated by the host (NVIDIA refuses binding names GenFramebuffers did not return; Hollow Knight drew black on edger)

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_685ed8fb0aed4f7099b7ecc34fc3b595

crates/gex-gl/native/gexgl-native.cpp

@@ -7,7 +7,8 @@
  *
  * Object names: the native host runs the guest's buffer, texture and other
  * names as they are (a desktop compatibility context and GLES both accept
- * names they never generated), so those tables are the identity; programs
+ * names they never generated), so those tables are the identity --
+ * except framebuffers and renderbuffers (gexgl_native_object); programs
  * and shaders are named by the host's GL, and host.rs tells this side about
  * each (gexgl_native_name). Program pipelines are generated by these cases
  * themselves and kept here. */
@@ -261,6 +262,28 @@ extern "C" void gexgl_native_pixel_store(uint32_t pname, int32_t param) {
     (void)gexgl_set_pixel_store(&pack_store, &unpack_store, pname, param);
 }
 
+/* A framebuffer (kind 2) or renderbuffer (kind 3) name of the guest's, as the
+ * host's: op 0 looks it up, generating a host name at its first use (a
+ * GenFramebuffers, or a bind of a name the guest never generated), op 1
+ * forgets it and says which host name to delete. 0 is 0. */
+extern "C" uint32_t gexgl_native_object(uint32_t kind, uint32_t guest, uint32_t op) {
+    if (!guest) return 0;
+    auto& map = kind == 2 ? framebuffers : renderbuffers;
+    auto it = map.find(guest);
+    if (op == 1) {
+        if (it == map.end()) return guest;
+        const GLuint host = it->second;
+        map.erase(it);
+        return host;
+    }
+    if (it != map.end()) return it->second;
+    GLuint host = 0;
+    if (kind == 2) glGenFramebuffers(1, &host);
+    else glGenRenderbuffers(1, &host);
+    map[guest] = host;
+    return host;
+}
+
 /* A shader (kind 0) or program (kind 1) host.rs created (host != 0) or
  * deleted (host == 0). */
 extern "C" void gexgl_native_name(uint32_t kind, uint32_t guest, uint32_t host) {

crates/gex-gl/native/hand-cases.inc

@@ -320,6 +320,11 @@
         /* Room for what GL writes even where the table says less. */
         std::vector<GLint> values(std::max<size_t>(n, 16));
         if (n) glGetIntegerv(pname, values.data());
+        /* The host's framebuffer and renderbuffer names, as the guest's. */
+        if (pname == GL_DRAW_FRAMEBUFFER_BINDING || pname == GL_READ_FRAMEBUFFER_BINDING)
+            values[0] = (GLint)external_name(framebuffers, (GLuint)values[0]);
+        if (pname == GL_RENDERBUFFER_BINDING)
+            values[0] = (GLint)external_name(renderbuffers, (GLuint)values[0]);
         put_blob(values.data(), n * sizeof(values[0]));
         break;
     }

crates/gex-gl/src/host.rs

@@ -1504,12 +1504,26 @@ impl Gl {
                     reply.u32(glGetError());
                 }
 
-                // Framebuffers. As for buffers and textures the guest picks
-                // the names, which binding accepts.
-                op::GEN_FRAMEBUFFERS | op::GEN_RENDERBUFFERS => {}
-                op::DELETE_FRAMEBUFFERS | op::DELETE_RENDERBUFFERS => {
+                // Framebuffers and renderbuffers are named by the host: unlike
+                // buffers and textures, ARB_framebuffer_object refuses a name
+                // GenFramebuffers did not return (NVIDIA does, with
+                // INVALID_OPERATION, and every FBO bind failed: Hollow Knight
+                // drew black there; Mesa takes them). The decoder keeps the
+                // map (`gexgl_native_object`), so the generated cases and the
+                // binding queries see the guest's names.
+                op::GEN_FRAMEBUFFERS | op::GEN_RENDERBUFFERS => {
+                    let kind = if opcode == op::GEN_FRAMEBUFFERS { 2 } else { 3 };
                     let n = a.u32().unwrap_or(0);
-                    let names: Vec<GLuint> = (0..n).filter_map(|_| a.u32()).collect();
+                    for _ in 0..n {
+                        if let Some(g) = a.u32() {
+                            native::gexgl_native_object(kind, g, 0);
+                        }
+                    }
+                }
+                op::DELETE_FRAMEBUFFERS | op::DELETE_RENDERBUFFERS => {
+                    let kind = if opcode == op::DELETE_FRAMEBUFFERS { 2 } else { 3 };
+                    let n = a.u32().unwrap_or(0);
+                    let names: Vec<GLuint> = (0..n).filter_map(|_| a.u32()).map(|g| native::gexgl_native_object(kind, g, 1)).collect();
                     if opcode == op::DELETE_FRAMEBUFFERS {
                         glDeleteFramebuffers(names.len() as GLsizei, names.as_ptr());
                     } else {
@@ -1518,12 +1532,12 @@ impl Gl {
                 }
                 op::BIND_FRAMEBUFFER => {
                     if let (Some(t), Some(n)) = (a.u32(), a.u32()) {
-                        glBindFramebuffer(t, n);
+                        glBindFramebuffer(t, native::gexgl_native_object(2, n, 0));
                     }
                 }
                 op::BIND_RENDERBUFFER => {
                     if let (Some(t), Some(n)) = (a.u32(), a.u32()) {
-                        glBindRenderbuffer(t, n);
+                        glBindRenderbuffer(t, native::gexgl_native_object(3, n, 0));
                     }
                 }
                 op::CHECK_FRAMEBUFFER_STATUS => {
@@ -1542,7 +1556,7 @@ impl Gl {
                     let (Some(t), Some(att), Some(rt), Some(rb)) = (a.u32(), a.u32(), a.u32(), a.u32()) else {
                         return true;
                     };
-                    glFramebufferRenderbuffer(t, att, rt, rb);
+                    glFramebufferRenderbuffer(t, att, rt, native::gexgl_native_object(3, rb, 0));
                 }
                 op::RENDERBUFFER_STORAGE => {
                     let (Some(t), Some(f), Some(w), Some(h)) = (a.u32(), a.u32(), a.i32(), a.i32()) else {
@@ -1754,6 +1768,7 @@ mod native {
         pub fn gexgl_native_one(op: u32, body: *const u8, len: usize, reply: *mut *const u8, reply_len: *mut usize) -> i32;
         pub fn gexgl_native_pixel_store(pname: u32, param: i32);
         pub fn gexgl_native_name(kind: u32, guest: u32, host: u32);
+        pub fn gexgl_native_object(kind: u32, guest: u32, op: u32) -> u32;
     }
 }