From a3a8a999b7f7c828992d76486ae38dc22a80a329 Mon Sep 17 00:00:00 2001
From: Sungun No <nors.nsg@gmail.com>
Date: Fri, 6 Jun 2025 20:40:57 +0900
Subject: [PATCH] gl_engine: fix always-true clear flag

The clear flag specified in Canvas::draw is ignored when set to false,
since GlRenderer::mClearBuffer is never explicitly reset to false.

This commit ensures that mClearBuffer is reset to its default (false)
after being used, so that the clear operation behaves correctly per frame.

- Issue: #1779
---
 src/renderer/gl_engine/tvgGlRenderTask.cpp | 29 ++++++++++------------
 src/renderer/gl_engine/tvgGlRenderTask.h   |  4 ++-
 src/renderer/gl_engine/tvgGlRenderer.cpp   |  5 +++-
 src/renderer/gl_engine/tvgGlRenderer.h     |  2 +-
 4 files changed, 21 insertions(+), 19 deletions(-)

diff --git a/src/renderer/gl_engine/tvgGlRenderTask.cpp b/src/renderer/gl_engine/tvgGlRenderTask.cpp
index c978febf..9cd206e2 100644
--- a/src/renderer/gl_engine/tvgGlRenderTask.cpp
+++ b/src/renderer/gl_engine/tvgGlRenderTask.cpp
@@ -195,23 +195,20 @@ void GlComposeTask::run()
 {
     GL_CHECK(glBindFramebuffer(GL_FRAMEBUFFER, getSelfFbo()));
 
-    // clear this fbo
-    if (mClearBuffer) {
-        // we must clear all area of fbo
-        GL_CHECK(glViewport(0, 0, mFbo->getWidth(), mFbo->getHeight()));
-        GL_CHECK(glScissor(0, 0, mFbo->getWidth(), mFbo->getHeight()));
-        GL_CHECK(glClearColor(0, 0, 0, 0));
-        GL_CHECK(glClearStencil(0));
-    #ifdef THORVG_GL_TARGET_GLES
-        GL_CHECK(glClearDepthf(0.0));
-    #else
-        GL_CHECK(glClearDepth(0.0));
-    #endif
-        GL_CHECK(glDepthMask(1));
+    // we must clear all area of fbo
+    GL_CHECK(glViewport(0, 0, mFbo->getWidth(), mFbo->getHeight()));
+    GL_CHECK(glScissor(0, 0, mFbo->getWidth(), mFbo->getHeight()));
+    GL_CHECK(glClearColor(0, 0, 0, 0));
+    GL_CHECK(glClearStencil(0));
+#ifdef THORVG_GL_TARGET_GLES
+    GL_CHECK(glClearDepthf(0.0));
+#else
+    GL_CHECK(glClearDepth(0.0));
+#endif
+    GL_CHECK(glDepthMask(1));
 
-        GL_CHECK(glClear(GL_COLOR_BUFFER_BIT | GL_STENCIL_BUFFER_BIT | GL_DEPTH_BUFFER_BIT));
-        GL_CHECK(glDepthMask(0));
-    }
+    GL_CHECK(glClear(GL_COLOR_BUFFER_BIT | GL_STENCIL_BUFFER_BIT | GL_DEPTH_BUFFER_BIT));
+    GL_CHECK(glDepthMask(0));
 
     GL_CHECK(glViewport(0, 0, mRenderWidth, mRenderHeight));
     GL_CHECK(glScissor(0, 0, mRenderWidth, mRenderHeight));
diff --git a/src/renderer/gl_engine/tvgGlRenderTask.h b/src/renderer/gl_engine/tvgGlRenderTask.h
index 6254292a..4c20f9cb 100644
--- a/src/renderer/gl_engine/tvgGlRenderTask.h
+++ b/src/renderer/gl_engine/tvgGlRenderTask.h
@@ -125,8 +125,8 @@ public:
     void run() override;
 
     void setRenderSize(uint32_t width, uint32_t height) { mRenderWidth = width; mRenderHeight = height; }
+    void setClearBuffer(bool clearBuffer) { mClearBuffer = clearBuffer; }
 
-    bool mClearBuffer = true;
 
 protected:
     GLuint getTargetFbo() { return mTargetFbo; }
@@ -134,6 +134,8 @@ protected:
     GLuint getResolveFboId();
     void onResolve();
 
+    bool mClearBuffer = false;
+
 private:
     GLuint mTargetFbo;
     GlRenderTarget* mFbo;
diff --git a/src/renderer/gl_engine/tvgGlRenderer.cpp b/src/renderer/gl_engine/tvgGlRenderer.cpp
index c9148145..0cac512a 100644
--- a/src/renderer/gl_engine/tvgGlRenderer.cpp
+++ b/src/renderer/gl_engine/tvgGlRenderer.cpp
@@ -839,7 +839,7 @@ bool GlRenderer::sync()
 
     prepareBlitTask(task);
 
-    task->mClearBuffer = mClearBuffer;
+    task->setClearBuffer(mClearBuffer);
     task->setTargetViewport({{0, 0}, {int32_t(surface.w), int32_t(surface.h)}});
 
     if (mGpuBuffer.flushToGPU()) {
@@ -853,6 +853,9 @@ bool GlRenderer::sync()
 
     clearDisposes();
 
+    // Reset clear buffer flag to default (false) after use.    
+    mClearBuffer = false; 
+
     delete task;
 
     return true;
diff --git a/src/renderer/gl_engine/tvgGlRenderer.h b/src/renderer/gl_engine/tvgGlRenderer.h
index 7ab1e901..1f29c5fa 100644
--- a/src/renderer/gl_engine/tvgGlRenderer.h
+++ b/src/renderer/gl_engine/tvgGlRenderer.h
@@ -153,7 +153,7 @@ private:
     } mDisposed;
 
     BlendMethod mBlendMethod = BlendMethod::Normal;
-    bool mClearBuffer = true;  //FIXME: clear buffer should be optional (default is false)
+    bool mClearBuffer = false;
 };
 
 #endif /* _TVG_GL_RENDERER_H_ */