[core] add ability show visualize the depth buffer to the GLFW and macOS app

3 files changed, 43 insertions, 0 deletions

diff --git a/src/mbgl/renderer/painter.cpp b/src/mbgl/renderer/painter.cpp
index 8500a946fd..163095d85b 100644
--- a/src/mbgl/renderer/painter.cpp
+++ b/src/mbgl/renderer/painter.cpp
@@ -198,6 +198,12 @@ void Painter::render(const Style& style, const FrameData& frame_, SpriteAtlas& a
         }
     }
 
+#ifndef NDEBUG
+    if (frame.debugOptions & MapDebugOptions::DepthBuffer) {
+        renderDepthBuffer();
+    }
+#endif
+
     // TODO: Find a better way to unbind VAOs after we're done with them without introducing
     // unnecessary bind(0)/bind(N) sequences.
     {
diff --git a/src/mbgl/renderer/painter.hpp b/src/mbgl/renderer/painter.hpp
index 2b6c1efdea..119155e011 100644
--- a/src/mbgl/renderer/painter.hpp
+++ b/src/mbgl/renderer/painter.hpp
@@ -89,6 +89,8 @@ public:
 #ifndef NDEBUG
     // Renders tile clip boundaries, using stencil buffer to calculate fill color.
     void renderClipMasks();
+    // Renders the depth buffer.
+    void renderDepthBuffer();
 #endif
 
     void renderDebugText(Tile&, const mat4&);
diff --git a/src/mbgl/renderer/painter_debug.cpp b/src/mbgl/renderer/painter_debug.cpp
index d6336b843c..7c24f67fb4 100644
--- a/src/mbgl/renderer/painter_debug.cpp
+++ b/src/mbgl/renderer/painter_debug.cpp
@@ -125,4 +125,39 @@ void Painter::renderClipMasks() {
 }
 #endif // NDEBUG
 
+#ifndef NDEBUG
+void Painter::renderDepthBuffer() {
+    config.stencilTest = GL_FALSE;
+    config.depthTest = GL_FALSE;
+    config.program = 0;
+    config.colorMask = { GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE };
+
+#ifndef GL_ES_VERSION_2_0
+    config.pixelZoom = { 1, 1 };
+    config.rasterPos = {{ -1, -1, 0, 0 }};
+
+    // Read the stencil buffer
+    const auto& fbSize = frame.framebufferSize;
+    auto pixels = std::make_unique<GLubyte[]>(fbSize[0] * fbSize[1]);
+
+    const double base = 1.0 / (1.0 - depthRangeSize);
+    glPixelTransferf(GL_DEPTH_SCALE, base);
+    glPixelTransferf(GL_DEPTH_BIAS, 1.0 - base);
+
+    MBGL_CHECK_ERROR(glReadPixels(
+                0,                  // GLint x
+                0,                  // GLint y
+                fbSize[0],          // GLsizei width
+                fbSize[1],          // GLsizei height
+                GL_DEPTH_COMPONENT, // GLenum format
+                GL_UNSIGNED_BYTE,   // GLenum type
+                pixels.get()        // GLvoid * data
+                ));
+
+    MBGL_CHECK_ERROR(glWindowPos2i(0, 0));
+    MBGL_CHECK_ERROR(glDrawPixels(fbSize[0], fbSize[1], GL_LUMINANCE, GL_UNSIGNED_BYTE, pixels.get()));
+#endif // GL_ES_VERSION_2_0
+}
+#endif // NDEBUG
+
 } // namespace mbgl