From 171d522bbbd60d783709399e009b7821590bb61e Mon Sep 17 00:00:00 2001
From: Michael Baetgen <michael@widerup.com>
Date: Sun, 8 Mar 2026 22:17:39 -0500
Subject: [PATCH] Fix: ensure to preserve gl state of calling application

---
 .../MilkdropPreset/MilkdropPreset.cpp         |   7 +-
 src/libprojectM/ProjectM.cpp                  |  12 +-
 src/libprojectM/Renderer/CMakeLists.txt       |   1 +
 src/libprojectM/Renderer/CopyTexture.cpp      |  15 +-
 src/libprojectM/Renderer/Framebuffer.cpp      |  30 +++-
 src/libprojectM/Renderer/Framebuffer.hpp      |  14 ++
 src/libprojectM/Renderer/GLStateGuard.hpp     | 131 ++++++++++++++++++
 src/libprojectM/Renderer/PresetTransition.cpp |   2 +-
 src/libprojectM/Renderer/VertexBuffer.hpp     |   3 +
 9 files changed, 204 insertions(+), 11 deletions(-)
 create mode 100644 src/libprojectM/Renderer/GLStateGuard.hpp

diff --git a/src/libprojectM/MilkdropPreset/MilkdropPreset.cpp b/src/libprojectM/MilkdropPreset/MilkdropPreset.cpp
index ef1716115b..abc9df1762 100755
--- a/src/libprojectM/MilkdropPreset/MilkdropPreset.cpp
+++ b/src/libprojectM/MilkdropPreset/MilkdropPreset.cpp
@@ -237,12 +237,17 @@ void MilkdropPreset::Load(std::istream& stream)
 
 void MilkdropPreset::InitializePreset(PresetFileParser& parsedFile)
 {
+    // Save the currently bound framebuffer so we can restore it after creating attachments.
+    // This is important when the host application uses a non-default framebuffer.
+    GLint previousFramebuffer{};
+    glGetIntegerv(GL_FRAMEBUFFER_BINDING, &previousFramebuffer);
+
     // Create the offscreen rendering surfaces.
     m_motionVectorUVMap = std::make_shared<Renderer::TextureAttachment>(GL_RG16F, GL_RG, GL_FLOAT, 0, 0);
     m_framebuffer.CreateColorAttachment(0, 0); // Main image 1
     m_framebuffer.CreateColorAttachment(1, 0); // Main image 2
 
-    Renderer::Framebuffer::Unbind();
+    glBindFramebuffer(GL_FRAMEBUFFER, previousFramebuffer);
 
     // Load global init variables into the state
     m_state.Initialize(parsedFile);
diff --git a/src/libprojectM/ProjectM.cpp b/src/libprojectM/ProjectM.cpp
index 9ec73afac7..91ea260898 100644
--- a/src/libprojectM/ProjectM.cpp
+++ b/src/libprojectM/ProjectM.cpp
@@ -29,6 +29,7 @@
 #include <Audio/PCM.hpp>
 
 #include <Renderer/CopyTexture.hpp>
+#include <Renderer/GLStateGuard.hpp>
 #include <Renderer/PresetTransition.hpp>
 #include <Renderer/ShaderCache.hpp>
 #include <Renderer/TextureManager.hpp>
@@ -121,6 +122,12 @@ void ProjectM::RenderFrame(uint32_t targetFramebufferObject /*= 0*/)
         return;
     }
 
+    // Save the host application's OpenGL state so we can restore it after rendering.
+    // This is required when libprojectM is used inside a shared OpenGL context,
+    // e.g. a Qt QOpenGLWidget, where the host expects its GL state to be preserved.
+    // The guard's destructor restores all captured state when this scope ends.
+    Renderer::GLStateGuard glStateGuard;
+
     // Update FPS and other timer values.
     m_timeKeeper->UpdateTimers();
 
@@ -356,6 +363,9 @@ auto ProjectM::UserSpriteIdentifiers() const -> std::vector<uint32_t>
 
 void ProjectM::BurnInTexture(uint32_t openGlTextureId, int left, int top, int width, int height)
 {
+    GLint previousFramebuffer{};
+    glGetIntegerv(GL_FRAMEBUFFER_BINDING, &previousFramebuffer);
+
     if (m_activePreset)
     {
         m_activePreset->BindFramebuffer();
@@ -368,7 +378,7 @@ void ProjectM::BurnInTexture(uint32_t openGlTextureId, int left, int top, int wi
         m_textureCopier->Draw(*m_shaderCache, openGlTextureId, m_windowWidth, m_windowHeight, left, top, width, height);
     }
 
-    Renderer::Framebuffer::Unbind();
+    glBindFramebuffer(GL_FRAMEBUFFER, previousFramebuffer);
 }
 
 void ProjectM::SetPresetLocked(bool locked)
diff --git a/src/libprojectM/Renderer/CMakeLists.txt b/src/libprojectM/Renderer/CMakeLists.txt
index 9de0a624f8..5b381584f0 100644
--- a/src/libprojectM/Renderer/CMakeLists.txt
+++ b/src/libprojectM/Renderer/CMakeLists.txt
@@ -26,6 +26,7 @@ add_library(Renderer OBJECT
         FileScanner.hpp
         Framebuffer.cpp
         Framebuffer.hpp
+        GLStateGuard.hpp
         IdleTextures.hpp
         Mesh.cpp
         Mesh.hpp
diff --git a/src/libprojectM/Renderer/CopyTexture.cpp b/src/libprojectM/Renderer/CopyTexture.cpp
index 14b36c977e..09f0aa61fb 100644
--- a/src/libprojectM/Renderer/CopyTexture.cpp
+++ b/src/libprojectM/Renderer/CopyTexture.cpp
@@ -104,6 +104,9 @@ void CopyTexture::Draw(ShaderCache& shaderCache,
         return;
     }
 
+    GLint previousFramebuffer{};
+    glGetIntegerv(GL_FRAMEBUFFER_BINDING, &previousFramebuffer);
+
     std::shared_ptr<class Texture> internalTexture;
 
     m_framebuffer.Bind(0);
@@ -125,7 +128,7 @@ void CopyTexture::Draw(ShaderCache& shaderCache,
         m_framebuffer.GetAttachment(0, TextureAttachment::AttachmentType::Color, 0)->Texture(internalTexture);
     }
 
-    Framebuffer::Unbind();
+    glBindFramebuffer(GL_FRAMEBUFFER, previousFramebuffer);
 }
 
 void CopyTexture::Draw(ShaderCache& shaderCache,
@@ -148,6 +151,9 @@ void CopyTexture::Draw(ShaderCache& shaderCache,
         return;
     }
 
+    GLint previousFramebuffer{};
+    glGetIntegerv(GL_FRAMEBUFFER_BINDING, &previousFramebuffer);
+
     m_framebuffer.Bind(0);
 
     // Draw from unflipped texture
@@ -162,7 +168,7 @@ void CopyTexture::Draw(ShaderCache& shaderCache,
     m_framebuffer.RemoveColorAttachment(0, 0);
     m_framebuffer.SetAttachment(0, 0, tempAttachment);
 
-    Framebuffer::Unbind();
+    glBindFramebuffer(GL_FRAMEBUFFER, previousFramebuffer);
 }
 
 void CopyTexture::Draw(ShaderCache& shaderCache,
@@ -186,6 +192,9 @@ void CopyTexture::Draw(ShaderCache& shaderCache,
         return;
     }
 
+    GLint previousFramebuffer{};
+    glGetIntegerv(GL_FRAMEBUFFER_BINDING, &previousFramebuffer);
+
     std::shared_ptr<class Texture> internalTexture;
 
     m_framebuffer.Bind(0);
@@ -200,7 +209,7 @@ void CopyTexture::Draw(ShaderCache& shaderCache,
     // Rebind our internal texture.
     m_framebuffer.GetAttachment(0, TextureAttachment::AttachmentType::Color, 0)->Texture(internalTexture);
 
-    Framebuffer::Unbind();
+    glBindFramebuffer(GL_FRAMEBUFFER, previousFramebuffer);
 }
 
 void CopyTexture::Draw(ShaderCache& shaderCache,
diff --git a/src/libprojectM/Renderer/Framebuffer.cpp b/src/libprojectM/Renderer/Framebuffer.cpp
index 29994d19f4..0fc443f53f 100644
--- a/src/libprojectM/Renderer/Framebuffer.cpp
+++ b/src/libprojectM/Renderer/Framebuffer.cpp
@@ -78,6 +78,11 @@ void Framebuffer::Unbind()
     glBindFramebuffer(GL_DRAW_FRAMEBUFFER, 0);
 }
 
+void Framebuffer::Unbind(GLuint defaultFramebufferObject)
+{
+    glBindFramebuffer(GL_DRAW_FRAMEBUFFER, defaultFramebufferObject);
+}
+
 bool Framebuffer::SetSize(int width, int height)
 {
     if (width == 0 || height == 0 ||
@@ -86,6 +91,9 @@ bool Framebuffer::SetSize(int width, int height)
         return false;
     }
 
+    GLint previousFramebuffer{};
+    glGetIntegerv(GL_FRAMEBUFFER_BINDING, &previousFramebuffer);
+
     m_width = width;
     m_height = height;
 
@@ -98,7 +106,7 @@ bool Framebuffer::SetSize(int width, int height)
             glFramebufferTexture2D(GL_FRAMEBUFFER, texture.first, GL_TEXTURE_2D, texture.second->Texture()->TextureID(), 0);
         }
     }
-    glBindFramebuffer(GL_FRAMEBUFFER, 0);
+    glBindFramebuffer(GL_FRAMEBUFFER, previousFramebuffer);
 
     return true;
 }
@@ -202,6 +210,9 @@ void Framebuffer::CreateColorAttachment(int framebufferIndex, int attachmentInde
         return;
     }
 
+    GLint previousFramebuffer{};
+    glGetIntegerv(GL_FRAMEBUFFER_BINDING, &previousFramebuffer);
+
     auto textureAttachment = std::make_shared<TextureAttachment>(internalFormat, format, type, m_width, m_height);
     const auto texture = textureAttachment->Texture();
     m_attachments.at(framebufferIndex).insert({GL_COLOR_ATTACHMENT0 + attachmentIndex, std::move(textureAttachment)});
@@ -212,7 +223,7 @@ void Framebuffer::CreateColorAttachment(int framebufferIndex, int attachmentInde
         glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0 + attachmentIndex, GL_TEXTURE_2D, texture->TextureID(), 0);
     }
     UpdateDrawBuffers(framebufferIndex);
-    glBindFramebuffer(GL_FRAMEBUFFER, 0);
+    glBindFramebuffer(GL_FRAMEBUFFER, previousFramebuffer);
 }
 
 void Framebuffer::RemoveColorAttachment(int framebufferIndex, int attachmentIndex)
@@ -243,6 +254,9 @@ void Framebuffer::CreateDepthAttachment(int framebufferIndex)
         return;
     }
 
+    GLint previousFramebuffer{};
+    glGetIntegerv(GL_FRAMEBUFFER_BINDING, &previousFramebuffer);
+
     auto textureAttachment = std::make_shared<TextureAttachment>(TextureAttachment::AttachmentType::Depth, m_width, m_height);
     const auto texture = textureAttachment->Texture();
     m_attachments.at(framebufferIndex).insert({GL_DEPTH_ATTACHMENT, std::move(textureAttachment)});
@@ -253,7 +267,7 @@ void Framebuffer::CreateDepthAttachment(int framebufferIndex)
         glFramebufferTexture2D(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_TEXTURE_2D, texture->TextureID(), 0);
     }
     UpdateDrawBuffers(framebufferIndex);
-    glBindFramebuffer(GL_FRAMEBUFFER, 0);
+    glBindFramebuffer(GL_FRAMEBUFFER, previousFramebuffer);
 }
 
 void Framebuffer::RemoveDepthAttachment(int framebufferIndex)
@@ -268,6 +282,9 @@ void Framebuffer::CreateStencilAttachment(int framebufferIndex)
         return;
     }
 
+    GLint previousFramebuffer{};
+    glGetIntegerv(GL_FRAMEBUFFER_BINDING, &previousFramebuffer);
+
     auto textureAttachment = std::make_shared<TextureAttachment>(TextureAttachment::AttachmentType::Stencil, m_width, m_height);
     const auto texture = textureAttachment->Texture();
     m_attachments.at(framebufferIndex).insert({GL_STENCIL_ATTACHMENT, std::move(textureAttachment)});
@@ -278,7 +295,7 @@ void Framebuffer::CreateStencilAttachment(int framebufferIndex)
         glFramebufferTexture2D(GL_FRAMEBUFFER, GL_STENCIL_ATTACHMENT, GL_TEXTURE_2D, texture->TextureID(), 0);
     }
     UpdateDrawBuffers(framebufferIndex);
-    glBindFramebuffer(GL_FRAMEBUFFER, 0);
+    glBindFramebuffer(GL_FRAMEBUFFER, previousFramebuffer);
 }
 
 void Framebuffer::RemoveStencilAttachment(int framebufferIndex)
@@ -293,6 +310,9 @@ void Framebuffer::CreateDepthStencilAttachment(int framebufferIndex)
         return;
     }
 
+    GLint previousFramebuffer{};
+    glGetIntegerv(GL_FRAMEBUFFER_BINDING, &previousFramebuffer);
+
     auto textureAttachment = std::make_shared<TextureAttachment>(TextureAttachment::AttachmentType::DepthStencil, m_width, m_height);
     const auto texture = textureAttachment->Texture();
     m_attachments.at(framebufferIndex).insert({GL_DEPTH_STENCIL_ATTACHMENT, std::move(textureAttachment)});
@@ -303,7 +323,7 @@ void Framebuffer::CreateDepthStencilAttachment(int framebufferIndex)
         glFramebufferTexture2D(GL_FRAMEBUFFER, GL_DEPTH_STENCIL_ATTACHMENT, GL_TEXTURE_2D, texture->TextureID(), 0);
     }
     UpdateDrawBuffers(framebufferIndex);
-    glBindFramebuffer(GL_FRAMEBUFFER, 0);
+    glBindFramebuffer(GL_FRAMEBUFFER, previousFramebuffer);
 }
 
 void Framebuffer::RemoveDepthStencilAttachment(int framebufferIndex)
diff --git a/src/libprojectM/Renderer/Framebuffer.hpp b/src/libprojectM/Renderer/Framebuffer.hpp
index 25bf28d41a..2167a30143 100644
--- a/src/libprojectM/Renderer/Framebuffer.hpp
+++ b/src/libprojectM/Renderer/Framebuffer.hpp
@@ -78,9 +78,23 @@ class Framebuffer
 
     /**
      * @brief Binds the default framebuffer for both reading and writing.
+     *
+     * When using libprojectM inside a shared OpenGL context,
+     * the default framebuffer may not be FBO 0. Use the overloaded version with the
+     * actual default FBO ID in such cases.
      */
     static void Unbind();
 
+    /**
+     * @brief Binds the given framebuffer ID as the current read/write framebuffer.
+     *
+     * This overload should be used when the host application's default framebuffer
+     * object is not 0.
+     *
+     * @param defaultFramebufferObject The framebuffer ID to bind.
+     */
+    static void Unbind(GLuint defaultFramebufferObject);
+
     /**
      * @brief Sets the framebuffer texture size.
      *
diff --git a/src/libprojectM/Renderer/GLStateGuard.hpp b/src/libprojectM/Renderer/GLStateGuard.hpp
new file mode 100644
index 0000000000..c6ddc8894f
--- /dev/null
+++ b/src/libprojectM/Renderer/GLStateGuard.hpp
@@ -0,0 +1,131 @@
+/**
+ * @file GLStateGuard.hpp
+ * @brief RAII guard that saves and restores OpenGL state around a rendering scope.
+ *
+ * This is used to ensure libprojectM doesn't leak GL state into the host
+ * application's rendering pipeline. This is especially important when hosted
+ * inside a shared OpenGL context such as Qt's QOpenGLWidget.
+ */
+#pragma once
+
+#include "OpenGL.h"
+
+namespace libprojectM {
+namespace Renderer {
+
+/**
+ * @brief RAII guard that captures OpenGL state on construction and restores it on destruction.
+ *
+ * Create an instance at the beginning of a rendering scope. When the instance goes out
+ * of scope (or is explicitly destroyed), all captured state is restored.
+ */
+class GLStateGuard
+{
+public:
+    /**
+     * @brief Captures the current OpenGL state.
+     */
+    GLStateGuard()
+    {
+        glGetIntegerv(GL_FRAMEBUFFER_BINDING, &m_framebuffer);
+        glGetIntegerv(GL_VERTEX_ARRAY_BINDING, &m_vertexArray);
+        glGetIntegerv(GL_CURRENT_PROGRAM, &m_program);
+        glGetIntegerv(GL_ACTIVE_TEXTURE, &m_activeTexture);
+        glGetIntegerv(GL_ARRAY_BUFFER_BINDING, &m_arrayBuffer);
+        glGetIntegerv(GL_ELEMENT_ARRAY_BUFFER_BINDING, &m_elementArrayBuffer);
+        glGetBooleanv(GL_BLEND, &m_blend);
+        glGetBooleanv(GL_DEPTH_TEST, &m_depthTest);
+        glGetIntegerv(GL_BLEND_SRC_RGB, &m_blendSrcRgb);
+        glGetIntegerv(GL_BLEND_DST_RGB, &m_blendDstRgb);
+#ifndef USE_GLES
+        glGetBooleanv(GL_LINE_SMOOTH, &m_lineSmooth);
+#endif
+    }
+
+    /**
+     * @brief Restores the OpenGL state captured at construction time.
+     */
+    ~GLStateGuard()
+    {
+        // Restore framebuffer
+        glBindFramebuffer(GL_FRAMEBUFFER, m_framebuffer);
+
+        // Restore VAO (must be done before restoring buffer bindings)
+        glBindVertexArray(m_vertexArray);
+
+        // Restore shader program
+        glUseProgram(m_program);
+
+        // Restore active texture unit
+        glActiveTexture(m_activeTexture);
+
+        // Restore buffer bindings
+        glBindBuffer(GL_ARRAY_BUFFER, m_arrayBuffer);
+        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, m_elementArrayBuffer);
+
+        // Restore blend state
+        if (m_blend)
+        {
+            glEnable(GL_BLEND);
+        }
+        else
+        {
+            glDisable(GL_BLEND);
+        }
+        glBlendFunc(m_blendSrcRgb, m_blendDstRgb);
+
+        // Restore depth test state
+        if (m_depthTest)
+        {
+            glEnable(GL_DEPTH_TEST);
+        }
+        else
+        {
+            glDisable(GL_DEPTH_TEST);
+        }
+
+#ifndef USE_GLES
+        // Restore line smooth state
+        if (m_lineSmooth)
+        {
+            glEnable(GL_LINE_SMOOTH);
+        }
+        else
+        {
+            glDisable(GL_LINE_SMOOTH);
+        }
+#endif
+
+        // Reset color mask to default (projectM may have changed it via MaskDrawBuffer)
+        glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
+
+        // Unbind any sampler objects left bound by projectM on common texture units
+        for (GLuint unit = 0; unit < 8; unit++)
+        {
+            glBindSampler(unit, 0);
+        }
+    }
+
+    GLStateGuard(const GLStateGuard&) = delete;
+    GLStateGuard(GLStateGuard&&) = delete;
+    auto operator=(const GLStateGuard&) -> GLStateGuard& = delete;
+    auto operator=(GLStateGuard&&) -> GLStateGuard& = delete;
+
+private:
+    GLint m_framebuffer{};
+    GLint m_vertexArray{};
+    GLint m_program{};
+    GLint m_activeTexture{};
+    GLint m_arrayBuffer{};
+    GLint m_elementArrayBuffer{};
+    GLboolean m_blend{};
+    GLboolean m_depthTest{};
+    GLint m_blendSrcRgb{};
+    GLint m_blendDstRgb{};
+#ifndef USE_GLES
+    GLboolean m_lineSmooth{};
+#endif
+};
+
+} // namespace Renderer
+} // namespace libprojectM
diff --git a/src/libprojectM/Renderer/PresetTransition.cpp b/src/libprojectM/Renderer/PresetTransition.cpp
index e7060861ea..a1bb9e8591 100644
--- a/src/libprojectM/Renderer/PresetTransition.cpp
+++ b/src/libprojectM/Renderer/PresetTransition.cpp
@@ -124,7 +124,7 @@ void PresetTransition::Draw(const Preset& oldPreset,
 
     for (int i = 2; i < textureUnit; i++)
     {
-        noiseDescriptors[i - 2].Unbind(textureUnit);
+        noiseDescriptors[i - 2].Unbind(i);
     }
 
     Mesh::Unbind();
diff --git a/src/libprojectM/Renderer/VertexBuffer.hpp b/src/libprojectM/Renderer/VertexBuffer.hpp
index 62788bfc9e..55c3edd36e 100644
--- a/src/libprojectM/Renderer/VertexBuffer.hpp
+++ b/src/libprojectM/Renderer/VertexBuffer.hpp
@@ -284,6 +284,7 @@ void VertexBuffer<VT>::Update()
 
     if (m_vertices.empty())
     {
+        Unbind();
         return;
     }
 
@@ -296,6 +297,8 @@ void VertexBuffer<VT>::Update()
         glBufferData(GL_ARRAY_BUFFER, static_cast<GLsizei>(sizeof(VT) * m_vertices.size()), m_vertices.data(), VertexBufferUsageToGL(m_vboUsage));
         m_vboSize = m_vertices.size();
     }
+
+    Unbind();
 }
 
 template<class VT>