Fix race condition causing hangs and EGL import errors due to concurrent snapshot() calls

src/platform/linux/graphics.cpp

@@ -558,6 +558,36 @@ namespace egl {
     return rgb;
   }
 
+  /**
+   * @brief Creates a black RGB texture of the specified image size.
+   * @param img The image to use for texture sizing.
+   * @return The new RGB texture.
+   */
+  rgb_t
+  create_blank(platf::img_t &img) {
+    rgb_t rgb {
+      EGL_NO_DISPLAY,
+      EGL_NO_IMAGE,
+      gl::tex_t::make(1)
+    };
+
+    gl::ctx.BindTexture(GL_TEXTURE_2D, rgb->tex[0]);
+    gl::ctx.TexStorage2D(GL_TEXTURE_2D, 1, GL_RGBA8, img.width, img.height);
+    gl::ctx.BindTexture(GL_TEXTURE_2D, 0);
+
+    auto framebuf = gl::frame_buf_t::make(1);
+    framebuf.bind(&rgb->tex[0], &rgb->tex[0] + 1);
+
+    GLenum attachment = GL_COLOR_ATTACHMENT0;
+    gl::ctx.DrawBuffers(1, &attachment);
+    const GLuint rgb_black[] = { 0, 0, 0, 0 };
+    gl::ctx.ClearBufferuiv(GL_COLOR, 0, rgb_black);
+
+    gl_drain_errors;
+
+    return rgb;
+  }
+
   std::optional<nv12_t>
   import_target(display_t::pointer egl_display, std::array<file_t, nv12_img_t::num_fds> &&fds, const surface_descriptor_t &r8, const surface_descriptor_t &gr88) {
     EGLAttrib img_attr_planes[2][17] {

src/platform/linux/graphics.h

@@ -268,6 +268,9 @@ namespace egl {
     display_t::pointer egl_display,
     const surface_descriptor_t &xrgb);
 
+  rgb_t
+  create_blank(platf::img_t &img);
+
   std::optional<nv12_t>
   import_target(
     display_t::pointer egl_display,

src/platform/linux/vaapi.cpp

@@ -436,7 +436,11 @@ namespace va {
     convert(platf::img_t &img) override {
       auto &descriptor = (egl::img_descriptor_t &) img;
 
-      if (descriptor.sequence > sequence) {
+      if (descriptor.sequence == 0) {
+        // For dummy images, use a blank RGB texture instead of importing a DMA-BUF
+        rgb = egl::create_blank(img);
+      }
+      else if (descriptor.sequence > sequence) {
         sequence = descriptor.sequence;
 
         rgb = egl::rgb_t {};

src/platform/linux/wlgrab.cpp

@@ -313,6 +313,8 @@ namespace wl {
     alloc_img() override {
       auto img = std::make_shared<egl::img_descriptor_t>();
 
+      img->width = width;
+      img->height = height;
       img->sequence = 0;
       img->serial = std::numeric_limits<decltype(img->serial)>::max();
       img->data = nullptr;
@@ -334,16 +336,8 @@ namespace wl {
 
     int
     dummy_img(platf::img_t *img) override {
-      // TODO: stop cheating and give black image
+      // Empty images are recognized as dummies by the zero sequence number
-      if (!img) {
+      return 0;
-        return -1;
-      };
-      auto pull_dummy_img_callback = [&img](std::shared_ptr<platf::img_t> &img_out) -> bool {
-        img_out = img->shared_from_this();
-        return true;
-      };
-      std::shared_ptr<platf::img_t> img_out;
-      return snapshot(pull_dummy_img_callback, img_out, 1000ms, false) != platf::capture_e::ok;
     }
 
     std::uint64_t sequence {};