use pbo for picking buffers, restore picking for scenery nodes

gl/pbo.cpp

@@ -0,0 +1,51 @@
+#include "pbo.h"
+
+void gl::pbo::request_read(int x, int y, int lx, int ly)
+{
+    int s = lx * ly * 4;
+    if (s != size)
+        allocate(PIXEL_PACK_BUFFER, s, GL_STREAM_DRAW);
+    size = s;
+
+    data_ready = false;
+    sync.reset();
+
+    bind(PIXEL_PACK_BUFFER);
+    glReadPixels(x, y, lx, ly, GL_RGBA, GL_UNSIGNED_BYTE, 0);
+    unbind(PIXEL_PACK_BUFFER);
+
+    sync.emplace();
+}
+
+bool gl::pbo::read_data(int lx, int ly, uint8_t *data)
+{
+    is_busy();
+
+    if (!data_ready)
+        return false;
+
+    int s = lx * ly * 4;
+    if (s != size)
+        return false;
+
+    download(PIXEL_PACK_BUFFER, data, 0, s);
+    unbind(PIXEL_PACK_BUFFER);
+    data_ready = false;
+
+    return true;
+}
+
+bool gl::pbo::is_busy()
+{
+    if (!sync)
+        return false;
+
+    if (sync->is_signalled())
+    {
+        data_ready = true;
+        sync.reset();
+        return false;
+    }
+
+    return true;
+}