gl_engine: ensure the gl context switching

This only covers emscripten environment,
need to cover other system.

issue: #3023

Co-Authored-By: Hermet Park <hermet@lottiefiles.com>

src/bindings/wasm/tvgWasmLottieAnimation.cpp

@@ -188,7 +188,7 @@ struct TvgWgEngine : TvgEngineMethod
 
 struct TvgGLEngine : TvgEngineMethod
 {
-    uintptr_t context = 0;
+    EMSCRIPTEN_WEBGL_CONTEXT_HANDLE context = 0;
     ~TvgGLEngine() override
     {
     #ifdef THORVG_GL_RASTER_SUPPORT
@@ -227,9 +227,7 @@ struct TvgGLEngine : TvgEngineMethod
     void resize(Canvas* canvas, int w, int h) override
     {
     #ifdef THORVG_GL_RASTER_SUPPORT
-        emscripten_webgl_make_context_current(context);
-
-        static_cast<GlCanvas*>(canvas)->target(0, w, h, ColorSpace::ABGR8888S);
+        static_cast<GlCanvas*>(canvas)->target((void*)context, 0, w, h, ColorSpace::ABGR8888S);
     #endif
     }
 };

src/renderer/gl_engine/tvgGlCommon.h

@@ -44,6 +44,7 @@
 #include "tvgMath.h"
 
 #ifdef __EMSCRIPTEN__
+    #include <emscripten/html5_webgl.h>
     // query GL Error on WebGL is very slow, so disable it on WebGL
     #define GL_CHECK(x) x
 #else

src/renderer/gl_engine/tvgGlRenderer.cpp

@@ -74,6 +74,19 @@ void GlRenderer::flush()
 }
 
 
+void GlRenderer::currentContext()
+{
+#ifdef __EMSCRIPTEN__
+    auto targetContext = (EMSCRIPTEN_WEBGL_CONTEXT_HANDLE)mContext;
+    if (emscripten_webgl_get_current_context() != targetContext) {
+        emscripten_webgl_make_context_current(targetContext);
+    }
+#else
+    TVGERR("GL_ENGINE", "Maybe missing MakeCurrent() Call?");
+#endif
+}
+
+
 GlRenderer::GlRenderer()
 {
 }
@@ -785,9 +798,12 @@ bool GlRenderer::clear()
 }
 
 
-bool GlRenderer::target(int32_t id, uint32_t w, uint32_t h)
+bool GlRenderer::target(void* context, int32_t id, uint32_t w, uint32_t h)
 {
-    if (id == GL_INVALID_VALUE || w == 0 || h == 0) return false;
+    //assume the context zero is invalid
+    if (!context || id == GL_INVALID_VALUE || w == 0 || h == 0) return false;
+
+    currentContext();
 
     flush();
 
@@ -795,6 +811,7 @@ bool GlRenderer::target(int32_t id, uint32_t w, uint32_t h)
     surface.w = w;
     surface.h = h;
 
+    mContext = context;
     mTargetFboId = static_cast<GLint>(id);
 
     mRootTarget.mWidth = surface.w;
@@ -811,6 +828,8 @@ bool GlRenderer::sync()
     //nothing to be done.
     if (mRenderPassStack.empty()) return true;
 
+    currentContext();
+
     // Blend function for straight alpha
     GL_CHECK(glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA));
     GL_CHECK(glEnable(GL_BLEND));
@@ -860,6 +879,7 @@ RenderRegion GlRenderer::region(RenderData data)
 
 bool GlRenderer::preRender()
 {
+    currentContext();
     if (mPrograms.empty()) initShaders();
     mRenderPassStack.push(new GlRenderPass(&mRootTarget));
 
@@ -1235,6 +1255,7 @@ bool GlRenderer::viewport(const RenderRegion& vp)
 
 bool GlRenderer::preUpdate()
 {
+    currentContext();
     return true;
 }
 

src/renderer/gl_engine/tvgGlRenderer.h

@@ -79,7 +79,7 @@ public:
     ColorSpace colorSpace() override;
     const RenderSurface* mainSurface() override;
 
-    bool target(int32_t id, uint32_t w, uint32_t h);
+    bool target(void* context, int32_t id, uint32_t w, uint32_t h);
     bool sync() override;
     bool clear() override;
 
@@ -115,7 +115,9 @@ private:
     void endRenderPass(RenderCompositor* cmp);
 
     void flush();
+    void currentContext();
 
+    void* mContext = nullptr;
     RenderSurface surface;
     GLint mTargetFboId = 0;
     RenderRegion mViewport;

src/renderer/tvgGlCanvas.cpp

@@ -54,7 +54,7 @@ Result GlCanvas::target(void* context, int32_t id, uint32_t w, uint32_t h, Color
     auto renderer = static_cast<GlRenderer*>(pImpl->renderer);
     if (!renderer) return Result::MemoryCorruption;
 
-    if (!renderer->target(id, w, h)) return Result::Unknown;
+    if (!renderer->target(context, id, w, h)) return Result::Unknown;
     pImpl->vport = {0, 0, (int32_t)w, (int32_t)h};
     renderer->viewport(pImpl->vport);