Correct and revise OpenGL texture pooling (#2709)

src/mbgl/gl/context.cpp

@@ -98,6 +98,8 @@ Context::Context(RendererBackend& backend_)
 #if MLN_DRAWABLE_RENDERER
     uboAllocator = std::make_unique<gl::UniformBufferAllocator>();
 #endif
+
+    texturePool = std::make_unique<Texture2DPool>(this);
 }
 
 Context::~Context() noexcept {
@@ -105,6 +107,10 @@ Context::~Context() noexcept {
         backend.getThreadPool().runRenderJobs(true /* closeQueue */);
 
         reset();
+
+        // Delete all pooled resources while the context is still valid
+        texturePool.reset();
+
 #if !defined(NDEBUG)
         Log::Debug(Event::General, "Rendering Stats:\n" + stats.toString("\n"));
 #endif
@@ -265,18 +271,14 @@ void Context::verifyProgramLinkage(ProgramID program_) {
     throw std::runtime_error("program failed to link");
 }
 
-UniqueTexture Context::createUniqueTexture() {
+UniqueTexture Context::createUniqueTexture(const Size& size,
+                                           gfx::TexturePixelType format,
+                                           gfx::TextureChannelDataType type) {
     MLN_TRACE_FUNC();
 
-    if (pooledTextures.empty()) {
-        pooledTextures.resize(TextureMax);
-        MBGL_CHECK_ERROR(glGenTextures(TextureMax, pooledTextures.data()));
-        stats.numCreatedTextures += TextureMax;
-    }
+    assert(texturePool);
+    TextureID id = texturePool->alloc(size, format, type);
 
-    TextureID id = pooledTextures.back();
-    pooledTextures.pop_back();
-    stats.numActiveTextures++;
     // NOLINTNEXTLINE(performance-move-const-arg)
     return UniqueTexture{std::move(id), {this}};
 }
@@ -306,27 +308,13 @@ std::unique_ptr<gfx::TextureResource> Context::createTextureResource(const Size
                                                                      const gfx::TextureChannelDataType type) {
     MLN_TRACE_FUNC();
 
-    auto obj = createUniqueTexture();
-    int textureByteSize = gl::TextureResource::getStorageSize(size, format, type);
-    stats.memTextures += textureByteSize;
-    std::unique_ptr<gfx::TextureResource> resource = std::make_unique<gl::TextureResource>(std::move(obj),
-                                                                                           textureByteSize);
+    auto obj = createUniqueTexture(size, format, type);
+    std::unique_ptr<gfx::TextureResource> resource = std::make_unique<gl::TextureResource>(std::move(obj));
 
     // Always use texture unit 0 for manipulating it.
     activeTextureUnit = 0;
     texture[0] = static_cast<gl::TextureResource&>(*resource).texture;
 
-    // Creates an empty texture with the specified size and format.
-    MBGL_CHECK_ERROR(glTexImage2D(GL_TEXTURE_2D,
-                                  0,
-                                  Enum<gfx::TexturePixelType>::sizedFor(format, type),
-                                  size.width,
-                                  size.height,
-                                  0,
-                                  Enum<gfx::TexturePixelType>::to(format),
-                                  Enum<gfx::TextureChannelDataType>::to(type),
-                                  nullptr));
-
     // We are using clamp to edge here since OpenGL ES doesn't allow GL_REPEAT
     // on NPOT textures. We use those when the pixelRatio isn't a power of two,
     // e.g. on iPhone 6 Plus.
@@ -530,9 +518,10 @@ std::unique_ptr<gfx::DrawScopeResource> Context::createDrawScopeResource() {
 void Context::reset() {
     MLN_TRACE_FUNC();
 
-    std::copy(pooledTextures.begin(), pooledTextures.end(), std::back_inserter(abandonedTextures));
-    pooledTextures.resize(0);
     performCleanup();
+
+    // Delete all unused pooled resources
+    texturePool->shrink();
 }
 
 #if MLN_DRAWABLE_RENDERER
@@ -883,10 +872,8 @@ void Context::performCleanup() {
                     binding.setDirty();
                 }
             }
+            texturePool->release(id);
         }
-        MBGL_CHECK_ERROR(glDeleteTextures(int(abandonedTextures.size()), abandonedTextures.data()));
-        stats.numCreatedTextures -= int(abandonedTextures.size());
-        assert(stats.numCreatedTextures >= 0);
         abandonedTextures.clear();
     }
 
@@ -923,6 +910,8 @@ void Context::reduceMemoryUsage() {
     MLN_TRACE_FUNC_GL();
 
     performCleanup();
+    assert(texturePool);
+    texturePool->shrink();
 
     // Ensure that all pending actions are executed to ensure that they happen
     // before the app goes to the background.
@@ -949,5 +938,10 @@ void Context::clearStencilBuffer(const int32_t bits) {
     stats.stencilClears++;
 }
 
+Texture2DPool& Context::getTexturePool() {
+    assert(texturePool);
+    return *texturePool;
+}
+
 } // namespace gl
 } // namespace mbgl