applyGsDispEnv programs display read circuit 2 only

ps2xRuntime/src/lib/Kernel/Stubs/GS.cpp

@@ -1050,7 +1050,12 @@ namespace ps2_stubs
         }
 
         const uint32_t fbw = std::max<uint32_t>(1u, (w + 63u) / 64u);
-        const uint64_t pmode = makePmode(1u, 1u, 0u, 0u, 0u, 0x80u);
+        // Double-buffering drives read circuit 2 only: on swap, applyGsDispEnv
+        // programs DISPFB2/DISPLAY2 and never touches circuit 1. Enabling EN1
+        // here would advertise a circuit this path never programs, leaving the
+        // compositor to blend circuit 1's stale reset-default surface over the
+        // correct circuit-2 page. Seed EN2 only; circuit 1 stays guest-owned.
+        const uint64_t pmode = makePmode(0u, 1u, 0u, 0u, 0u, 0x80u);
         const uint64_t smode2 =
             (static_cast<uint64_t>(g_gparam.interlace & 0x1u) << 0) |
             (static_cast<uint64_t>(g_gparam.ffmode & 0x1u) << 1);
@@ -1121,7 +1126,12 @@ namespace ps2_stubs
         }
 
         const uint32_t fbw = std::max<uint32_t>(1u, (w + 63u) / 64u);
-        const uint64_t pmode = makePmode(1u, 1u, 0u, 0u, 0u, 0x80u);
+        // Double-buffering drives read circuit 2 only: on swap, applyGsDispEnv
+        // programs DISPFB2/DISPLAY2 and never touches circuit 1. Enabling EN1
+        // here would advertise a circuit this path never programs, leaving the
+        // compositor to blend circuit 1's stale reset-default surface over the
+        // correct circuit-2 page. Seed EN2 only; circuit 1 stays guest-owned.
+        const uint64_t pmode = makePmode(0u, 1u, 0u, 0u, 0u, 0x80u);
         const uint64_t smode2 =
             (static_cast<uint64_t>(g_gparam.interlace & 0x1u) << 0) |
             (static_cast<uint64_t>(g_gparam.ffmode & 0x1u) << 1);

ps2xRuntime/src/lib/Kernel/Stubs/Helpers/Support.h

@@ -1875,8 +1875,11 @@ namespace
         auto &regs = runtime->memory().gs();
         regs.pmode = env.pmode;
         regs.smode2 = env.smode2;
-        regs.dispfb1 = env.dispfb;
-        regs.display1 = env.display;
+        // Circuit 1 (DISPFB1/DISPLAY1) is NOT programmed here: sceGsPutDispEnv's
+        // env struct describes read circuit 2 only; the game drives circuit 1
+        // itself via GS privileged MMIO. Writing circuit 1 from the single-
+        // circuit env forces both read circuits onto the same surface and
+        // collapses any two-buffer blend (e.g. movie underlay + UI overlay).
         regs.dispfb2 = env.dispfb;
         regs.display2 = env.display;
         regs.bgcolor = env.bgcolor;

ps2xTest/src/ps2_gs_tests.cpp

@@ -459,12 +459,159 @@ void register_ps2_gs_tests()
             setRegU32(ctx, 5, 1u);
             ps2_stubs::sceGsSwapDBuffDc(rdram.data(), &ctx, &runtime);
 
-            t.Equals(runtime.memory().gs().dispfb1 & 0x1FFull, 151ull,
+            t.Equals(runtime.memory().gs().dispfb2 & 0x1FFull, 151ull,
                      "sceGsSwapDBuffDc should program GS to the selected display page");
-            t.Equals((runtime.memory().gs().display1 >> 32) & 0x0FFFull, 639ull,
+            t.Equals((runtime.memory().gs().display2 >> 32) & 0x0FFFull, 639ull,
                      "sceGsSwapDBuffDc should preserve the display width from the seeded env");
         });
 
+        tc.Run("sceGsSwapDBuffDc drives read circuit 2 only and preserves circuit 1", [](TestCase &t)
+        {
+            PS2Runtime runtime;
+            t.IsTrue(runtime.memory().initialize(), "runtime memory initialize should succeed");
+
+            // Seed distinct circuit-1 sentinels AFTER initialize(); reset
+            // defaults are fbw=10 / 639x447, so these differ from them.
+            runtime.memory().gs().dispfb1 = 0xDEADBEEFDEADBEEFull;
+            runtime.memory().gs().display1 = 0xCAFEF00DCAFEF00Dull;
+            runtime.memory().gs().pmode = 0u;
+
+            std::vector<uint8_t> rdram(PS2_RAM_SIZE, 0u);
+            constexpr uint32_t kEnvAddr = 0x7000u;
+            constexpr uint32_t kDBuffSize = 0x330u;
+
+            R5900Context ctx{};
+            setRegU32(ctx, 4, kEnvAddr);
+            setRegU32(ctx, 5, 0u);   // psm
+            setRegU32(ctx, 6, 640u); // width
+            setRegU32(ctx, 7, 448u); // height
+            std::memset(rdram.data() + kEnvAddr, 0xCD, kDBuffSize);
+            ps2_stubs::sceGsSetDefDBuffDc(rdram.data(), &ctx, &runtime);
+
+            std::memset(&ctx, 0, sizeof(ctx));
+            setRegU32(ctx, 4, kEnvAddr);
+            setRegU32(ctx, 5, 1u); // swap to page 1
+            ps2_stubs::sceGsSwapDBuffDc(rdram.data(), &ctx, &runtime);
+
+            // The double-buffer path programs read circuit 2 only. Its seeded
+            // PMODE must NOT enable read circuit 1 (EN1); otherwise the
+            // compositor blends the never-programmed circuit-1 surface (frozen
+            // at reset defaults) over the correct circuit-2 page.
+            t.Equals(runtime.memory().gs().pmode & 0x1ull, 0x0ull,
+                     "sceGsSwapDBuffDc must not enable read circuit 1 (EN1) in PMODE");
+            t.Equals(runtime.memory().gs().pmode & 0x2ull, 0x2ull,
+                     "sceGsSwapDBuffDc should enable read circuit 2 (EN2) in PMODE");
+
+            // The shared circuit-2-only helper must leave circuit 1 untouched.
+            t.Equals(runtime.memory().gs().dispfb1, 0xDEADBEEFDEADBEEFull,
+                     "sceGsSwapDBuffDc must not clobber circuit-1 DISPFB1");
+            t.Equals(runtime.memory().gs().display1, 0xCAFEF00DCAFEF00Dull,
+                     "sceGsSwapDBuffDc must not clobber circuit-1 DISPLAY1");
+        });
+
+        tc.Run("sceGsSwapDBuff drives read circuit 2 only and preserves circuit 1", [](TestCase &t)
+        {
+            PS2Runtime runtime;
+            t.IsTrue(runtime.memory().initialize(), "runtime memory initialize should succeed");
+
+            // Seed distinct circuit-1 sentinels AFTER initialize(); reset
+            // defaults are fbw=10 / 639x447, so these differ from them.
+            runtime.memory().gs().dispfb1 = 0xDEADBEEFDEADBEEFull;
+            runtime.memory().gs().display1 = 0xCAFEF00DCAFEF00Dull;
+            runtime.memory().gs().pmode = 0u;
+
+            std::vector<uint8_t> rdram(PS2_RAM_SIZE, 0u);
+            constexpr uint32_t kEnvAddr = 0x8000u;
+            constexpr uint32_t kDBuffSize = 0x330u;
+            constexpr uint32_t kStackAddr = 0xB00u;
+
+            R5900Context ctx{};
+            setRegU32(ctx, 4, kEnvAddr);
+            setRegU32(ctx, 5, 0u);   // psm
+            setRegU32(ctx, 6, 640u); // width
+            setRegU32(ctx, 7, 448u); // height
+            // sceGsSetDefDBuff (non-Dc) reads its trailing ztest/zpsm/clear
+            // args from the guest stack via sp+16/sp+20/sp+24, so sp (r29)
+            // must point at valid, zero-initialized rdram.
+            setRegU32(ctx, 29, kStackAddr);
+            std::memset(rdram.data() + kEnvAddr, 0xCD, kDBuffSize);
+            ps2_stubs::sceGsSetDefDBuff(rdram.data(), &ctx, &runtime);
+
+            std::memset(&ctx, 0, sizeof(ctx));
+            setRegU32(ctx, 4, kEnvAddr);
+            setRegU32(ctx, 5, 1u); // swap to page 1
+            ps2_stubs::sceGsSwapDBuff(rdram.data(), &ctx, &runtime);
+
+            // The double-buffer path programs read circuit 2 only. Its seeded
+            // PMODE must NOT enable read circuit 1 (EN1); otherwise the
+            // compositor blends the never-programmed circuit-1 surface (frozen
+            // at reset defaults) over the correct circuit-2 page.
+            t.Equals(runtime.memory().gs().pmode & 0x1ull, 0x0ull,
+                     "sceGsSwapDBuff must not enable read circuit 1 (EN1) in PMODE");
+            t.Equals(runtime.memory().gs().pmode & 0x2ull, 0x2ull,
+                     "sceGsSwapDBuff should enable read circuit 2 (EN2) in PMODE");
+
+            // The shared circuit-2-only helper must leave circuit 1 untouched.
+            t.Equals(runtime.memory().gs().dispfb1, 0xDEADBEEFDEADBEEFull,
+                     "sceGsSwapDBuff must not clobber circuit-1 DISPFB1");
+            t.Equals(runtime.memory().gs().display1, 0xCAFEF00DCAFEF00Dull,
+                     "sceGsSwapDBuff must not clobber circuit-1 DISPLAY1");
+        });
+
+        tc.Run("sceGsPutDispEnv programs read circuit 2 only and leaves circuit 1 untouched", [](TestCase &t)
+        {
+            PS2Runtime runtime;
+            t.IsTrue(runtime.memory().initialize(), "runtime memory initialize should succeed");
+
+            runtime.memory().gs().dispfb1 = 0xDEADBEEFDEADBEEFull;
+            runtime.memory().gs().display1 = 0xCAFEF00DCAFEF00Dull;
+            runtime.memory().gs().dispfb2 = 0u;
+            runtime.memory().gs().display2 = 0u;
+            runtime.memory().gs().pmode = 0u;
+            runtime.memory().gs().smode2 = 0u;
+            runtime.memory().gs().bgcolor = 0u;
+
+            std::vector<uint8_t> rdram(PS2_RAM_SIZE, 0u);
+            constexpr uint32_t kEnvAddr = 0x6000u;
+            constexpr uint32_t kPmodeOffset = 0u;
+            constexpr uint32_t kSmode2Offset = 8u;
+            constexpr uint32_t kDispFbOffset = 16u;
+            constexpr uint32_t kDisplayOffset = 24u;
+            constexpr uint32_t kBgColorOffset = 32u;
+
+            const uint64_t pmode = 0x8007ull;
+            const uint64_t smode2 = 0x1ull;
+            const uint64_t dispfb = 0x9070ull;
+            const uint64_t display = 0x1234000000005678ull;
+            const uint64_t bgcolor = 0x00445566ull;
+
+            std::memcpy(rdram.data() + kEnvAddr + kPmodeOffset, &pmode, sizeof(pmode));
+            std::memcpy(rdram.data() + kEnvAddr + kSmode2Offset, &smode2, sizeof(smode2));
+            std::memcpy(rdram.data() + kEnvAddr + kDispFbOffset, &dispfb, sizeof(dispfb));
+            std::memcpy(rdram.data() + kEnvAddr + kDisplayOffset, &display, sizeof(display));
+            std::memcpy(rdram.data() + kEnvAddr + kBgColorOffset, &bgcolor, sizeof(bgcolor));
+
+            R5900Context ctx{};
+            setRegU32(ctx, 4, kEnvAddr);
+            ps2_stubs::sceGsPutDispEnv(rdram.data(), &ctx, &runtime);
+
+            t.Equals(runtime.memory().gs().pmode, pmode,
+                     "sceGsPutDispEnv should program PMODE from the env");
+            t.Equals(runtime.memory().gs().smode2, smode2,
+                     "sceGsPutDispEnv should program SMODE2 from the env");
+            t.Equals(runtime.memory().gs().dispfb2, dispfb,
+                     "sceGsPutDispEnv should program DISPFB2 from the env");
+            t.Equals(runtime.memory().gs().display2, display,
+                     "sceGsPutDispEnv should program DISPLAY2 from the env");
+            t.Equals(runtime.memory().gs().bgcolor, bgcolor,
+                     "sceGsPutDispEnv should program BGCOLOR from the env");
+
+            t.Equals(runtime.memory().gs().dispfb1, 0xDEADBEEFDEADBEEFull,
+                     "sceGsPutDispEnv must not clobber circuit-1 DISPFB1");
+            t.Equals(runtime.memory().gs().display1, 0xCAFEF00DCAFEF00Dull,
+                     "sceGsPutDispEnv must not clobber circuit-1 DISPLAY1");
+        });
+
         tc.Run("sceGsSetDefDBuffDc seeds a clear packet and swap clears the draw buffer", [](TestCase &t)
         {
             PS2Runtime runtime;