[Fix] (DirectGLES): never leave a stale program bound when the new one is broken

When a shader stage fails to transpile or compile, SyncToBackend logs it and
carries on, so the program is linked without that stage - or does not link at
all. Use() then issued glUseProgram for it, which is an INVALID_OPERATION for an
unlinked program and, crucially, leaves the *previous* program current. The draw
went ahead and rendered with an entirely unrelated shader.

That is how KHR-GL3x.texture_size_promotion's GL_TEXTURE_RECTANGLE cases
produced 1.0 for a red channel: SPIRV-Cross refuses sampler2DRect for ESSL
("Rectangle textures are not supported on OpenGL ES"), so every rectangle
program was broken, and the draws kept running the previous case's 1D-array
alpha shader - whose alpha is 1.0. Wrong pixels from a shader the app never
bound are far worse to debug than a blank result.

The program now records whether the last sync produced something usable, and
Use() binds 0 rather than the broken program, making the draw a visible no-op.
The redundancy cache tracks whatever was actually bound, so it stays correct
across the switch.

Does not fix the rectangle cases themselves - those need a SPIR-V pass lowering
Dim::Rect to Dim::2D before SPIRV-Cross runs (plus the coordinate divide for
non-texelFetch lookups), alongside mapping the target to GL_TEXTURE_2D.

MobileGL/MG_Backend/DirectGLES/Managers.cpp

@@ -3258,6 +3258,7 @@ namespace MobileGL::MG_Backend::DirectGLES {
 
             MGLOG_D("Syncing program to backend. State program ID: %u, Backend ID: %u",
                     stateProgramObject->GetExternalIndex(), m_backendProgramId);
+            m_backendProgramUsable = true;
             m_snormFallbackClampOutputMask = g_snormFallbackClampOutputMask;
             m_unormFallbackClampOutputMask = g_unormFallbackClampOutputMask;
             m_fragColorBroadcastCount = g_fragColorBroadcastCount;
@@ -3365,6 +3366,7 @@ namespace MobileGL::MG_Backend::DirectGLES {
                     r.log += spvcSession.GetLastErrorString();
                     r.errc = -5;
                     MGLOG_E("%s", r.log.c_str());
+                    m_backendProgramUsable = false;
                     continue;
                 }
 
@@ -3406,6 +3408,7 @@ namespace MobileGL::MG_Backend::DirectGLES {
                     Vector<GLchar> log(logLength);
                     g_GLESFuncs.glGetShaderInfoLog(backendShaderId, logLength, nullptr, log.data());
                     MGLOG_E("Shader compilation failed for backend ID %u: %s", backendShaderId, log.data());
+                    m_backendProgramUsable = false;
                     continue;
                 }
 
@@ -3441,6 +3444,7 @@ namespace MobileGL::MG_Backend::DirectGLES {
 
             GLint linkStatus;
             g_GLESFuncs.glGetProgramiv(m_backendProgramId, GL_LINK_STATUS, &linkStatus);
+            m_backendProgramUsable = m_backendProgramUsable && linkStatus == GL_TRUE;
             if (linkStatus != GL_TRUE) {
                 GLint logLength;
                 g_GLESFuncs.glGetProgramiv(m_backendProgramId, GL_INFO_LOG_LENGTH, &logLength);
@@ -3566,12 +3570,18 @@ namespace MobileGL::MG_Backend::DirectGLES {
 #ifdef TRACY_ENABLE
             ZoneScopedC(TRACY_ZONECOLOR_BACKEND);
 #endif
-            if (g_lastUsedBackendProgramId == m_backendProgramId) {
+            // glUseProgram on a program that did not link is an INVALID_OPERATION and
+            // leaves the *previous* program current, so the draw would silently render
+            // with an unrelated shader (KHR-GL3x.texture_size_promotion read another
+            // test case's alpha that way once a sampler2DRect stage failed to
+            // transpile). Bind nothing instead: the draw is then a visible no-op.
+            const Uint programToBind = m_backendProgramUsable ? m_backendProgramId : 0;
+            if (g_lastUsedBackendProgramId == programToBind) {
                 return;
             }
-            MGLOG_D("Using program %u", m_backendProgramId);
-            g_GLESFuncs.glUseProgram(m_backendProgramId);
-            g_lastUsedBackendProgramId = m_backendProgramId;
+            MGLOG_D("Using program %u", programToBind);
+            g_GLESFuncs.glUseProgram(programToBind);
+            g_lastUsedBackendProgramId = programToBind;
         }
 
         void BackendProgramObjectImpl::SetBaseInstance(Uint32 baseInstance) const {

MobileGL/MG_Backend/DirectGLES/Managers.h

@@ -600,6 +600,10 @@ namespace MobileGL::MG_Backend::DirectGLES {
             void SetDrawID(Uint32 drawId) const;
             Int GetIndirectParamsBinding() const { return m_indirectParamsBinding; }
             Uint GetBackendProgramId() const { return m_backendProgramId; }
+            // False when the last SyncToBackend could not produce a usable program (a
+            // shader failed to transpile or compile, or the link itself failed). Use()
+            // must not leave the previously bound program current in that case.
+            Bool IsBackendProgramUsable() const { return m_backendProgramUsable; }
             Uint GetBackendGlobalUBOId() const { return m_backendGlobalUBOId; }
             Uint32 GetSnormFallbackClampOutputMask() const { return m_snormFallbackClampOutputMask; }
             Uint32 GetUnormFallbackClampOutputMask() const { return m_unormFallbackClampOutputMask; }
@@ -634,6 +638,7 @@ namespace MobileGL::MG_Backend::DirectGLES {
             // PrgramImpl::BroadcastLegacyFragColor); 1 keeps the plain single-output shader.
             Uint m_fragColorBroadcastCount = 1;
             Bool m_isInitialized = false;
+            Bool m_backendProgramUsable = false;
 
             Int m_globalUboBackendBlockIndex = -1;
             Int m_globalUboBackendBlockSize = 0;