[node] Move to using PBOs for the readStillImage call in HeadlessView.

1 files changed, 29 insertions, 10 deletions

diff --git a/platform/default/headless_view.cpp b/platform/default/headless_view.cpp
index 71fdf5885b..6f0d6c2198 100644
--- a/platform/default/headless_view.cpp
+++ b/platform/default/headless_view.cpp
@@ -49,23 +49,42 @@ PremultipliedImage HeadlessView::readStillImage() {
     const unsigned int h = dimensions[1] * pixelRatio;
 
     PremultipliedImage image { w, h };
+    GLuint bufferId;
+
+    MBGL_CHECK_ERROR(glGenBuffers(1, &bufferId));
+    MBGL_CHECK_ERROR(glBindBuffer(GL_PIXEL_PACK_BUFFER, bufferId));
+    MBGL_CHECK_ERROR(glBufferData(GL_PIXEL_PACK_BUFFER, h * image.stride(), 0, GL_STREAM_READ));
+
     {
         util::stopwatch stopwatch2("glReadPixels", EventSeverity::Info, Event::General);
-        MBGL_CHECK_ERROR(glReadPixels(0, 0, w, h, GL_RGBA, GL_UNSIGNED_BYTE, image.data.get()));
+        MBGL_CHECK_ERROR(glReadPixels(0, 0, w, h, GL_RGBA, GL_UNSIGNED_BYTE, 0));
     }
 
-    const auto stride = image.stride();
-    auto tmp = std::make_unique<uint8_t[]>(stride);
-    uint8_t* rgba = image.data.get();
-    {
-        util::stopwatch stopwatch3("memcpy", EventSeverity::Info, Event::General);
-        for (int i = 0, j = h - 1; i < j; i++, j--) {
-            std::memcpy(tmp.get(), rgba + i * stride, stride);
-            std::memcpy(rgba + i * stride, rgba + j * stride, stride);
-            std::memcpy(rgba + j * stride, tmp.get(), stride);
+    // map the PBO to process its data by CPU
+    GLubyte* ptr = (GLubyte*)glMapBuffer(GL_PIXEL_PACK_BUFFER, GL_READ_ONLY);
+
+    if (ptr) {
+        const int stride = image.stride();
+        auto tmp = std::make_unique<uint8_t[]>(stride);
+        uint8_t* rgba = image.data.get();
+
+        {
+            util::stopwatch stopwatch3("memcpy", EventSeverity::Info, Event::General);
+            for (unsigned int i = 0, j = h - 1; i < h; i++, j--) {
+                std::memcpy(rgba + i * stride, ptr + j * stride, stride);
+            }
         }
+
+        MBGL_CHECK_ERROR(glUnmapBuffer(GL_PIXEL_PACK_BUFFER));
+    } else {
+        throw std::runtime_error(std::string("Could not map buffer on return from read pixels."));
     }
 
+    MBGL_CHECK_ERROR(glDeleteBuffers(1, &bufferId));
+
+    // back to conventional pixel operation
+    MBGL_CHECK_ERROR(glBindBuffer(GL_PIXEL_PACK_BUFFER, 0));
+
     return image;
 }