use pbo for picking buffers, restore picking for scenery nodes

gl/buffer.cpp

@@ -64,4 +64,19 @@ void gl::buffer::upload(targets target, const void *data, int offset, int size)
     glBufferSubData(glenum_target(target), offset, size, data);
 }
 
+void gl::buffer::download(targets target, void *data, int offset, int size)
+{
+    bind(target);
+    if (GLAD_GL_VERSION_3_3)
+    {
+        glGetBufferSubData(glenum_target(target), offset, size, data);
+    }
+    else
+    {
+        void *glbuf = glMapBufferRange(glenum_target(target), offset, size, GL_MAP_READ_BIT);
+        memcpy(data, glbuf, size);
+        glUnmapBuffer(glenum_target(target));
+    }
+}
+
 GLuint gl::buffer::binding_points[13];

gl/buffer.h

@@ -40,5 +40,6 @@ namespace gl
 
         void allocate(targets target, int size, GLenum hint);
         void upload(targets target, const void *data, int offset, int size);
+        void download(targets target, void *data, int offset, int size);
     };
 }

gl/fence.cpp

@@ -12,7 +12,8 @@ gl::fence::~fence()
 
 bool gl::fence::is_signalled()
 {
+    GLsizei len = 0;
     GLint val;
-    glGetSynciv(sync, GL_SYNC_STATUS, 1, &val);
-    return val == GL_SIGNALED;
+    glGetSynciv(sync, GL_SYNC_STATUS, 1, &len, &val);
+    return len == 1 && val == GL_SIGNALED;
 }

gl/fence.h

@@ -11,5 +11,8 @@ namespace gl
         ~fence();
 
         bool is_signalled();
+
+        fence(const fence&) = delete;
+        fence& operator=(const fence&) = delete;
     };
 }

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;
+}

gl/pbo.h

@@ -0,0 +1,17 @@
+#include "buffer.h"
+#include "fence.h"
+#include <optional>
+
+namespace gl {
+    class pbo : private buffer
+    {
+        std::optional<fence> sync;
+        int size = 0;
+        bool data_ready;
+
+    public:
+        void request_read(int x, int y, int lx, int ly);
+        bool read_data(int lx, int ly, uint8_t *data);
+        bool is_busy();
+    };
+}