Refactor TransformState to use internal 3d camera

2 files changed, 257 insertions, 0 deletions

diff --git a/src/mbgl/util/camera.cpp b/src/mbgl/util/camera.cpp
new file mode 100644
index 0000000000..f64e24ab2d
--- /dev/null
+++ b/src/mbgl/util/camera.cpp
@@ -0,0 +1,215 @@
+#include "camera.hpp"
+#include <cassert>
+#include <cmath>
+#include <mbgl/map/camera.hpp>
+#include <mbgl/math/log2.hpp>
+#include <mbgl/util/constants.hpp>
+#include <mbgl/util/geo.hpp>
+#include <mbgl/util/projection.hpp>
+
+namespace mbgl {
+
+namespace {
+double vec2Len(const vec2& v) {
+    return std::sqrt(v[0] * v[0] + v[1] * v[1]);
+};
+
+double vec2Dot(const vec2& a, const vec2& b) {
+    return a[0] * b[0] + a[1] * b[1];
+};
+
+vec2 vec2Scale(const vec2& v, double s) {
+    return vec2{{v[0] * s, v[1] * s}};
+};
+} // namespace
+
+namespace util {
+
+static double mercatorXfromLng(double lng) {
+    return (180.0 + lng) / 360.0;
+}
+
+static double mercatorYfromLat(double lat) {
+    return (180.0 - (180.0 / M_PI * std::log(std::tan(M_PI_4 + lat * M_PI / 360.0)))) / 360.0;
+}
+
+static double latFromMercatorY(double y) {
+    return util::RAD2DEG * (2.0 * std::atan(std::exp(M_PI - y * util::M2PI)) - M_PI_2);
+}
+
+static double lngFromMercatorX(double x) {
+    return x * 360.0 - 180.0;
+}
+
+static double* getColumn(mat4& matrix, int col) {
+    assert(col >= 0 && col < 4);
+    return &matrix[col * 4];
+}
+
+static const double* getColumn(const mat4& matrix, int col) {
+    assert(col >= 0 && col < 4);
+    return &matrix[col * 4];
+}
+
+static vec3 toMercator(const LatLng& location, double altitudeMeters) {
+    const double pixelsPerMeter = 1.0 / Projection::getMetersPerPixelAtLatitude(location.latitude(), 0.0);
+    const double worldSize = Projection::worldSize(std::pow(2.0, 0.0));
+
+    return {{mercatorXfromLng(location.longitude()),
+             mercatorYfromLat(location.latitude()),
+             altitudeMeters * pixelsPerMeter / worldSize}};
+}
+
+static Quaternion orientationFromPitchBearing(double pitch, double bearing) {
+    // Both angles have to be negated to achieve CW rotation around the axis of rotation
+    Quaternion rotBearing = Quaternion::fromAxisAngle({{0.0, 0.0, 1.0}}, -bearing);
+    Quaternion rotPitch = Quaternion::fromAxisAngle({{1.0, 0.0, 0.0}}, -pitch);
+
+    return rotBearing.multiply(rotPitch);
+}
+
+static void updateTransform(mat4& transform, const Quaternion& orientation) {
+    // Construct rotation matrix from orientation
+    mat4 m = orientation.toRotationMatrix();
+
+    // Apply translation to the matrix
+    double* col = getColumn(m, 3);
+
+    col[0] = getColumn(transform, 3)[0];
+    col[1] = getColumn(transform, 3)[1];
+    col[2] = getColumn(transform, 3)[2];
+
+    transform = m;
+}
+
+static void updateTransform(mat4& transform, const vec3& position) {
+    getColumn(transform, 3)[0] = position[0];
+    getColumn(transform, 3)[1] = position[1];
+    getColumn(transform, 3)[2] = position[2];
+}
+
+Camera::Camera() : orientation(Quaternion::identity) {
+    matrix::identity(transform);
+}
+
+vec3 Camera::getPosition() const {
+    const double* p = getColumn(transform, 3);
+    return {{p[0], p[1], p[2]}};
+}
+
+mat4 Camera::getCameraToWorld(double scale, bool flippedY) const {
+    mat4 cameraToWorld;
+    matrix::invert(cameraToWorld, getWorldToCamera(scale, flippedY));
+    return cameraToWorld;
+}
+
+mat4 Camera::getWorldToCamera(double scale, bool flippedY) const {
+    // transformation chain from world space to camera space:
+    // 1. Height value (z) of renderables is in meters. Scale z coordinate by pixelsPerMeter
+    // 2. Transform from pixel coordinates to camera space with cameraMatrix^-1
+    // 3. flip Y if required
+
+    // worldToCamera: flip * cam^-1 * zScale
+    // cameraToWorld: (flip * cam^-1 * zScale)^-1 => (zScale^-1 * cam * flip^-1)
+    const double worldSize = Projection::worldSize(scale);
+    const double latitude = latFromMercatorY(getColumn(transform, 3)[1]);
+    const double pixelsPerMeter = worldSize / (std::cos(latitude * util::DEG2RAD) * util::M2PI * util::EARTH_RADIUS_M);
+
+    // Compute inverse of the camera matrix
+    mat4 result = orientation.conjugate().toRotationMatrix();
+
+    matrix::translate(
+        result, result, -transform[12] * worldSize, -transform[13] * worldSize, -transform[14] * worldSize);
+
+    if (!flippedY) {
+        // Pre-multiply y
+        result[1] *= -1.0;
+        result[5] *= -1.0;
+        result[9] *= -1.0;
+        result[13] *= -1.0;
+    }
+
+    // Post-multiply z
+    result[8] *= pixelsPerMeter;
+    result[9] *= pixelsPerMeter;
+    result[10] *= pixelsPerMeter;
+    result[11] *= pixelsPerMeter;
+
+    return result;
+}
+
+mat4 Camera::getCameraToClipPerspective(double fovy, double aspectRatio, double nearZ, double farZ) const {
+    mat4 projection;
+    matrix::perspective(projection, fovy, aspectRatio, nearZ, farZ);
+    return projection;
+}
+
+vec3 Camera::forward() const {
+    const double* column = getColumn(transform, 2);
+    // The forward direction is towards the map, [0, 0, -1]
+    return {{-column[0], -column[1], -column[2]}};
+}
+
+vec3 Camera::right() const {
+    const double* column = getColumn(transform, 0);
+    return {{column[0], column[1], column[2]}};
+}
+
+vec3 Camera::up() const {
+    const double* column = getColumn(transform, 1);
+    // Up direction has to be flipped due to y-axis pointing towards south
+    return {{-column[0], -column[1], -column[2]}};
+}
+
+void Camera::getOrientation(double& pitch, double& bearing) const {
+    const vec3 f = forward();
+    const vec3 r = right();
+
+    bearing = std::atan2(-r[1], r[0]);
+    pitch = std::atan2(std::sqrt(f[0] * f[0] + f[1] * f[1]), -f[2]);
+}
+
+void Camera::setOrientation(double pitch, double bearing) {
+    orientation = orientationFromPitchBearing(pitch, bearing);
+    updateTransform(transform, orientation);
+}
+
+void Camera::setOrientation(const Quaternion& orientation_) {
+    orientation = orientation_;
+    updateTransform(transform, orientation);
+}
+
+void Camera::setPosition(const vec3& position) {
+    updateTransform(transform, position);
+}
+
+optional<Quaternion> Camera::orientationFromFrame(const vec3& forward, const vec3& up) {
+    vec3 upVector = up;
+
+    vec2 xyForward = {{forward[0], forward[1]}};
+    vec2 xyUp = {{up[0], up[1]}};
+    const double epsilon = 1e-15;
+
+    // Remove roll-component of the resulting orientation by projecting
+    // the up-vector to the forward vector on xy-plane
+    if (vec2Len(xyForward) >= epsilon) {
+        const vec2 xyDir = vec2Scale(xyForward, 1.0 / vec2Len(xyForward));
+
+        xyUp = vec2Scale(xyDir, vec2Dot(xyUp, xyDir));
+        upVector[0] = xyUp[0];
+        upVector[1] = xyUp[1];
+    }
+
+    const vec3 right = vec3Cross(upVector, forward);
+
+    if (vec3Length(right) < epsilon) {
+        return nullopt;
+    }
+
+    const double bearing = std::atan2(-right[1], right[0]);
+    const double pitch = std::atan2(std::sqrt(forward[0] * forward[0] + forward[1] * forward[1]), -forward[2]);
+
+    return util::orientationFromPitchBearing(pitch, bearing);
+}
+} // namespace util
+} // namespace mbgl
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diff --git a/src/mbgl/util/camera.hpp b/src/mbgl/util/camera.hpp
new file mode 100644
index 0000000000..030d7cfaac
--- /dev/null
+++ b/src/mbgl/util/camera.hpp
@@ -0,0 +1,42 @@
+#pragma once
+
+#include <mbgl/util/optional.hpp>
+#include <mbgl/util/size.hpp>
+#include "quaternion.hpp"
+
+namespace mbgl {
+
+class LatLng;
+
+namespace util {
+
+class Camera {
+public:
+    Camera();
+
+    vec3 getPosition() const;
+    mat4 getCameraToWorld(double scale, bool flippedY) const;
+    mat4 getWorldToCamera(double scale, bool flippedY) const;
+    mat4 getCameraToClipPerspective(double fovy, double aspectRatio, double nearZ, double farZ) const;
+
+    vec3 forward() const;
+    vec3 right() const;
+    vec3 up() const;
+
+    const Quaternion& getOrientation() const { return orientation; }
+    void getOrientation(double& pitch, double& bearing) const;
+    void setOrientation(double pitch, double bearing);
+    void setOrientation(const Quaternion& orientation_);
+    void setPosition(const vec3& position);
+
+    // Computes orientation using forward and up vectors of the provided coordinate frame.
+    // Only bearing and pitch components will be used. Does not return a value if input is invalid
+    static optional<Quaternion> orientationFromFrame(const vec3& forward, const vec3& up);
+
+private:
+    Quaternion orientation;
+    mat4 transform; // Position (mercator) and orientation of the camera
+};
+
+} // namespace util
+} // namespace mbgl
\ No newline at end of file