Add method to render window contents to picture file (opengl)

dgl/Window.hpp

@@ -382,6 +382,13 @@ public:
     */
     void repaint(const Rectangle<uint>& rect) noexcept;
 
+   /**
+      Render this window's content into a picture file, specified by @a filename.
+      Window must be visible and on screen.
+      Written picture format is PPM.
+    */
+    void renderToPicture(const char* filename);
+
    /**
       Run this window as a modal, blocking input events from the parent.
       Only valid for windows that have been created with another window as parent (as passed in the constructor).

dgl/src/Cairo.cpp

@@ -808,6 +808,13 @@ void TopLevelWidget::PrivateData::display()
 
 // -----------------------------------------------------------------------
 
+void Window::PrivateData::renderToPicture(const char*, const GraphicsContext&, uint, uint)
+{
+    notImplemented("Window::PrivateData::renderToPicture");
+}
+
+// -----------------------------------------------------------------------
+
 const GraphicsContext& Window::PrivateData::getGraphicsContext() const noexcept
 {
     GraphicsContext& context((GraphicsContext&)graphicsContext);

dgl/src/OpenGL.cpp

@@ -667,6 +667,34 @@ void TopLevelWidget::PrivateData::display()
 
 // -----------------------------------------------------------------------
 
+void Window::PrivateData::renderToPicture(const char* const filename,
+                                          const GraphicsContext&,
+                                          const uint width,
+                                          const uint height)
+{
+    FILE* const f = fopen(filename, "w");
+    DISTRHO_SAFE_ASSERT_RETURN(f != nullptr,);
+
+    GLubyte* const pixels = new GLubyte[width * height * 3 * sizeof(GLubyte)];
+
+    glFlush();
+    glReadPixels(0, 0, width, height, GL_RGB, GL_UNSIGNED_BYTE, pixels);
+
+    fprintf(f, "P3\n%d %d\n255\n", width, height);
+    for (uint y = 0; y < height; y++) {
+        for (uint i, x = 0; x < width; x++) {
+            i = 3 * ((height - y - 1) * width + x);
+            fprintf(f, "%3d %3d %3d ", pixels[i], pixels[i+1], pixels[i+2]);
+        }
+        fprintf(f, "\n");
+    }
+
+    delete[] pixels;
+    fclose(f);
+}
+
+// -----------------------------------------------------------------------
+
 const GraphicsContext& Window::PrivateData::getGraphicsContext() const noexcept
 {
     return (const GraphicsContext&)graphicsContext;

dgl/src/Vulkan.cpp

@@ -231,6 +231,13 @@ void TopLevelWidget::PrivateData::display()
 
 // -----------------------------------------------------------------------
 
+void Window::PrivateData::renderToPicture(const char*, const GraphicsContext&, uint, uint)
+{
+    notImplemented("Window::PrivateData::renderToPicture");
+}
+
+// -----------------------------------------------------------------------
+
 const GraphicsContext& Window::PrivateData::getGraphicsContext() const noexcept
 {
     return (const GraphicsContext&)graphicsContext;

dgl/src/Window.cpp

@@ -336,6 +336,11 @@ void Window::repaint(const Rectangle<uint>& rect) noexcept
     puglPostRedisplayRect(pData->view, prect);
 }
 
+void Window::renderToPicture(const char* const filename)
+{
+    pData->filenameToRenderInto = strdup(filename);
+}
+
 void Window::runAsModal(bool blockWait)
 {
     pData->runAsModal(blockWait);

dgl/src/WindowPrivateData.cpp

@@ -95,6 +95,7 @@ Window::PrivateData::PrivateData(Application& a, Window* const s)
       minHeight(0),
       keepAspectRatio(false),
       ignoreIdleCallbacks(false),
+      filenameToRenderInto(nullptr),
 #ifdef DISTRHO_OS_WINDOWS
       win32SelectedFile(nullptr),
 #endif
@@ -120,6 +121,7 @@ Window::PrivateData::PrivateData(Application& a, Window* const s, PrivateData* c
       minHeight(0),
       keepAspectRatio(false),
       ignoreIdleCallbacks(false),
+      filenameToRenderInto(nullptr),
 #ifdef DISTRHO_OS_WINDOWS
       win32SelectedFile(nullptr),
 #endif
@@ -149,6 +151,7 @@ Window::PrivateData::PrivateData(Application& a, Window* const s,
       minHeight(0),
       keepAspectRatio(false),
       ignoreIdleCallbacks(false),
+      filenameToRenderInto(nullptr),
 #ifdef DISTRHO_OS_WINDOWS
       win32SelectedFile(nullptr),
 #endif
@@ -180,6 +183,7 @@ Window::PrivateData::PrivateData(Application& a, Window* const s,
       minHeight(0),
       keepAspectRatio(false),
       ignoreIdleCallbacks(false),
+      filenameToRenderInto(nullptr),
 #ifdef DISTRHO_OS_WINDOWS
       win32SelectedFile(nullptr),
 #endif
@@ -195,6 +199,7 @@ Window::PrivateData::~PrivateData()
 {
     appData->idleCallbacks.remove(this);
     appData->windows.remove(self);
+    std::free(filenameToRenderInto);
 
     if (view == nullptr)
         return;
@@ -744,6 +749,14 @@ void Window::PrivateData::onPuglExpose()
             widget->pData->display();
     }
 #endif
+
+    if (char* const filename = filenameToRenderInto)
+    {
+        const PuglRect rect = puglGetFrame(view);
+        filenameToRenderInto = nullptr;
+        renderToPicture(filename, getGraphicsContext(), static_cast<uint>(rect.width), static_cast<uint>(rect.height));
+        std::free(filename);
+    }
 }
 
 void Window::PrivateData::onPuglClose()

dgl/src/WindowPrivateData.hpp

@@ -77,6 +77,9 @@ struct Window::PrivateData : IdleCallback {
     /** Whether to ignore idle callback requests, useful for temporary windows. */
     bool ignoreIdleCallbacks;
 
+    /** Render to a picture file when non-null, automatically free+unset after saving. */
+    char* filenameToRenderInto;
+
 #ifdef DISTRHO_OS_WINDOWS
     /** Selected file for openFileBrowser on windows, stored for fake async operation. */
     const char* win32SelectedFile;
@@ -162,6 +165,8 @@ struct Window::PrivateData : IdleCallback {
 # endif
 #endif
 
+    static void renderToPicture(const char* filename, const GraphicsContext& context, uint width, uint height);
+
     // modal handling
     void startModal();
     void stopModal();