[core] add state tracking to pixel transfer

src/mbgl/gl/context.cpp

@@ -285,6 +285,8 @@ void Context::setDirtyState() {
     rasterPos.setDirty();
     pixelStorePack.setDirty();
     pixelStoreUnpack.setDirty();
+    pixelTransferDepth.setDirty();
+    pixelTransferStencil.setDirty();
 #endif // MBGL_USE_GLES2
     for (auto& tex : texture) {
        tex.setDirty();

src/mbgl/gl/context.hpp

@@ -132,6 +132,8 @@ public:
     State<value::RasterPos> rasterPos;
     State<value::PixelStorePack> pixelStorePack;
     State<value::PixelStoreUnpack> pixelStoreUnpack;
+    State<value::PixelTransferDepth> pixelTransferDepth;
+    State<value::PixelTransferStencil> pixelTransferStencil;
 #endif // MBGL_USE_GLES2
 
 private:

src/mbgl/gl/value.cpp

@@ -417,6 +417,34 @@ PixelStoreUnpack::Type PixelStoreUnpack::Get() {
     return value;
 }
 
+const constexpr PixelTransferDepth::Type PixelTransferDepth::Default;
+
+void PixelTransferDepth::Set(const Type& value) {
+    MBGL_CHECK_ERROR(glPixelTransferf(GL_DEPTH_SCALE, value.scale));
+    MBGL_CHECK_ERROR(glPixelTransferf(GL_DEPTH_BIAS, value.bias));
+}
+
+PixelTransferDepth::Type PixelTransferDepth::Get() {
+    Type value;
+    MBGL_CHECK_ERROR(glGetFloatv(GL_DEPTH_SCALE, &value.scale));
+    MBGL_CHECK_ERROR(glGetFloatv(GL_DEPTH_BIAS, &value.bias));
+    return value;
+}
+
+const constexpr PixelTransferStencil::Type PixelTransferStencil::Default;
+
+void PixelTransferStencil::Set(const Type& value) {
+    MBGL_CHECK_ERROR(glPixelTransferf(GL_INDEX_SHIFT, value.shift));
+    MBGL_CHECK_ERROR(glPixelTransferf(GL_INDEX_OFFSET, value.offset));
+}
+
+PixelTransferStencil::Type PixelTransferStencil::Get() {
+    Type value;
+    MBGL_CHECK_ERROR(glGetIntegerv(GL_INDEX_SHIFT, &value.shift));
+    MBGL_CHECK_ERROR(glGetIntegerv(GL_INDEX_OFFSET, &value.offset));
+    return value;
+}
+
 #endif // MBGL_USE_GLES2
 
 } // namespace value

src/mbgl/gl/value.hpp

@@ -282,6 +282,34 @@ struct PixelStoreUnpack {
     static Type Get();
 };
 
+struct PixelTransferDepth {
+    struct Type {
+        float scale;
+        float bias;
+    };
+    static const constexpr Type Default = { 1, 0 };
+    static void Set(const Type&);
+    static Type Get();
+};
+
+constexpr bool operator!=(const PixelTransferDepth::Type& a, const PixelTransferDepth::Type& b) {
+    return a.scale != b.scale || a.bias != b.bias;
+}
+
+struct PixelTransferStencil {
+    struct Type {
+        int32_t shift;
+        int32_t offset;
+    };
+    static const constexpr Type Default = { 0, 0 };
+    static void Set(const Type&);
+    static Type Get();
+};
+
+constexpr bool operator!=(const PixelTransferStencil::Type& a, const PixelTransferStencil::Type& b) {
+    return a.shift != b.shift || a.offset != b.offset;
+}
+
 #endif // MBGL_USE_GLES2
 
 } // namespace value

src/mbgl/renderer/painter_debug.cpp

@@ -73,6 +73,9 @@ void Painter::renderClipMasks(PaintParameters&) {
     // tightly packed into the buffer to avoid buffer overruns. Also see unpacking adjustment below.
     context.pixelStorePack = { 1 };
 
+    // Reset the value in case someone else changed it, or it's dirty.
+    context.pixelTransferStencil = gl::value::PixelTransferStencil::Default;
+
     // Read the stencil buffer
     const auto viewport = context.viewport.getCurrentValue();
     auto pixels = std::make_unique<uint8_t[]>(viewport.size.width * viewport.size.height);
@@ -116,9 +119,8 @@ void Painter::renderDepthBuffer(PaintParameters&) {
 
     // Scales the values in the depth buffer so that they cover the entire grayscale range. This
     // makes it easier to spot tiny differences.
-    const double base = 1.0 / (1.0 - depthRangeSize);
-    MBGL_CHECK_ERROR(glPixelTransferf(GL_DEPTH_SCALE, base));
-    MBGL_CHECK_ERROR(glPixelTransferf(GL_DEPTH_BIAS, 1.0 - base));
+    const float base = 1.0f / (1.0f - depthRangeSize);
+    context.pixelTransferDepth = { base, 1.0f - base };
 
     // Read the stencil buffer
     auto viewport = context.viewport.getCurrentValue();