From 8d22e2bf017c1442a15b1fbe404dff77fb21e8fc Mon Sep 17 00:00:00 2001
From: Ansis Brammanis <brammanis@gmail.com>
Date: Fri, 14 Aug 2015 12:41:18 +0300
Subject: [PATCH] port perspective projection matrix from -js

---
 src/mbgl/map/transform_state.cpp | 21 ++++++++++-----------
 src/mbgl/map/transform_state.hpp | 11 ++++++++---
 src/mbgl/renderer/gl_config.hpp  |  1 +
 src/mbgl/renderer/painter.cpp    | 23 +++++++++++++++++++++--
 4 files changed, 40 insertions(+), 16 deletions(-)

diff --git a/src/mbgl/map/transform_state.cpp b/src/mbgl/map/transform_state.cpp
index 9a5e53092..1cb1d9f82 100644
--- a/src/mbgl/map/transform_state.cpp
+++ b/src/mbgl/map/transform_state.cpp
@@ -10,19 +10,11 @@ using namespace mbgl;
 
 void TransformState::matrixFor(mat4& matrix, const TileID& id, const int8_t z) const {
     const double tile_scale = std::pow(2, z);
-    const double tile_size = scale * util::tileSize / tile_scale;
+    double s = util::tileSize * scale / tile_scale;
 
     matrix::identity(matrix);
-
-    matrix::translate(matrix, matrix, 0.5f * (float)width, 0.5f * (float)height, 0);
-    matrix::rotate_z(matrix, matrix, angle);
-    matrix::translate(matrix, matrix, -0.5f * (float)width, -0.5f * (float)height, 0);
-
-    matrix::translate(matrix, matrix, pixel_x() + id.x * tile_size, pixel_y() + id.y * tile_size, 0);
-
-    // TODO: Get rid of the 8 (scaling from 4096 to tile size);
-    float factor = scale / tile_scale / (4096.0f / util::tileSize);
-    matrix::scale(matrix, matrix, factor, factor, 1);
+    matrix::translate(matrix, matrix, id.x * s, id.y * s, 0);
+    matrix::scale(matrix, matrix, s / 4096.0f, s / 4096.0f, 1);
 }
 
 box TransformState::cornersToBox(uint32_t z) const {
@@ -154,6 +146,13 @@ float TransformState::getAngle() const {
     return angle;
 }
 
+float TransformState::getAltitude() const {
+    return altitude;
+}
+
+float TransformState::getPitch() const {
+    return pitch;
+}
 
 #pragma mark - Projection
 
diff --git a/src/mbgl/map/transform_state.hpp b/src/mbgl/map/transform_state.hpp
index 16f2de2f7..3996e6e54 100644
--- a/src/mbgl/map/transform_state.hpp
+++ b/src/mbgl/map/transform_state.hpp
@@ -49,6 +49,9 @@ public:
     // Rotation
     float getAngle() const;
 
+    float getAltitude() const;
+    float getPitch() const;
+
     // Projection
     const vec2<double> pixelForLatLng(const LatLng latLng) const;
     const LatLng latLngForPixel(const vec2<double> pixel) const;
@@ -56,6 +59,9 @@ public:
     // Changing
     bool isChanging() const;
 
+    double pixel_x() const;
+    double pixel_y() const;
+
 private:
     void constrain(double& scale, double& y) const;
 
@@ -63,9 +69,6 @@ private:
     double min_scale = std::pow(2, 0);
     double max_scale = std::pow(2, 18);
 
-    double pixel_x() const;
-    double pixel_y() const;
-
     // logical dimensions
     uint16_t width = 0, height = 0;
 
@@ -80,6 +83,8 @@ private:
     double x = 0, y = 0;
     double angle = 0;
     double scale = 1;
+    double altitude = 1.5;
+    double pitch = 0;
 
     // cache values for spherical mercator math
     double Bc = (scale * util::tileSize) / 360;
diff --git a/src/mbgl/renderer/gl_config.hpp b/src/mbgl/renderer/gl_config.hpp
index 59507f721..2389293a4 100644
--- a/src/mbgl/renderer/gl_config.hpp
+++ b/src/mbgl/renderer/gl_config.hpp
@@ -117,6 +117,7 @@ struct DepthTest {
     static const Type Default;
     inline static void Set(const Type& value) {
         MBGL_CHECK_ERROR(value ? glEnable(GL_DEPTH_TEST) : glDisable(GL_DEPTH_TEST));
+        MBGL_CHECK_ERROR(glDisable(GL_DEPTH_TEST));
     }
 };
 
diff --git a/src/mbgl/renderer/painter.cpp b/src/mbgl/renderer/painter.cpp
index b55b71dcb..4b5503bcc 100644
--- a/src/mbgl/renderer/painter.cpp
+++ b/src/mbgl/renderer/painter.cpp
@@ -132,8 +132,27 @@ void Painter::lineWidth(float line_width) {
 }
 
 void Painter::changeMatrix() {
-    // Initialize projection matrix
-    matrix::ortho(projMatrix, 0, state.getWidth(), state.getHeight(), 0, -1, 1);
+
+    double halfFov = std::atan(0.5 / state.getAltitude());
+    double topHalfSurfaceDistance = std::sin(halfFov) * state.getAltitude() /
+        std::sin(M_PI / 2.0f - state.getPitch() - halfFov);
+    // Calculate z value of the farthest fragment that should be rendered.
+    double farZ = std::cos(M_PI / 2.0f - state.getPitch()) * topHalfSurfaceDistance + state.getAltitude();
+
+    matrix::perspective(projMatrix, 2.0f * std::atan((state.getHeight() / 2.0f) / state.getAltitude()),
+            double(state.getWidth()) / state.getHeight(), 0.1, farZ);
+
+    matrix::translate(projMatrix, projMatrix, 0, 0, -state.getAltitude());
+
+    // After the rotateX, z values are in pixel units. Convert them to
+    // altitude unites. 1 altitude unit = the screen height.
+    matrix::scale(projMatrix, projMatrix, 1, -1, 1.0f / state.getHeight());
+
+    matrix::rotate_x(projMatrix, projMatrix, state.getPitch());
+    matrix::rotate_z(projMatrix, projMatrix, state.getAngle());
+
+    matrix::translate(projMatrix, projMatrix, state.pixel_x() - state.getWidth() / 2.0f,
+            state.pixel_y() - state.getWidth() / 2.0f, 0);
 
     // The extrusion matrix.
     matrix::identity(extrudeMatrix);