fix symbol rendering in perspective view

7 files changed, 84 insertions, 21 deletions

diff --git a/src/mbgl/renderer/painter.cpp b/src/mbgl/renderer/painter.cpp
index 4b5503bcca..7f06b2345c 100644
--- a/src/mbgl/renderer/painter.cpp
+++ b/src/mbgl/renderer/painter.cpp
@@ -155,9 +155,7 @@ void Painter::changeMatrix() {
             state.pixel_y() - state.getWidth() / 2.0f, 0);
 
     // The extrusion matrix.
-    matrix::identity(extrudeMatrix);
-    matrix::multiply(extrudeMatrix, projMatrix, extrudeMatrix);
-    matrix::rotate_z(extrudeMatrix, extrudeMatrix, state.getAngle());
+    matrix::ortho(extrudeMatrix, 0, state.getWidth(), state.getHeight(), 0, 0, -1);
 
     // The native matrix is a 1:1 matrix that paints the coordinates at the
     // same screen position as the vertex specifies.
diff --git a/src/mbgl/renderer/painter_symbol.cpp b/src/mbgl/renderer/painter_symbol.cpp
index 5c2db77096..c64f32620a 100644
--- a/src/mbgl/renderer/painter_symbol.cpp
+++ b/src/mbgl/renderer/painter_symbol.cpp
@@ -28,25 +28,40 @@ void Painter::renderSDF(SymbolBucket &bucket,
 {
     mat4 vtxMatrix = translatedMatrix(matrix, styleProperties.translate, id, styleProperties.translate_anchor);
 
-    mat4 exMatrix;
-    matrix::copy(exMatrix, projMatrix);
-
     bool aligned_with_map = (bucketProperties.rotation_alignment == RotationAlignmentType::Map);
-    const float angleOffset = aligned_with_map ? state.getAngle() : 0;
-
-    if (angleOffset) {
-        matrix::rotate_z(exMatrix, exMatrix, angleOffset);
+    bool skewed = aligned_with_map;
+    mat4 exMatrix;
+    float s;
+    float gammaScale;
+
+    if (skewed) {
+        matrix::identity(exMatrix);
+        s = 4096.0f / util::tileSize / id.overscaling / std::pow(2, state.getZoom() - id.z);
+        gammaScale = 1.0f / std::cos(state.getPitch());
+    } else {
+        exMatrix = extrudeMatrix;
+        s = state.getAltitude();
+        gammaScale = 1.0f;
     }
+    matrix::scale(exMatrix, exMatrix, s, s, 1);
 
     // If layerStyle.size > bucket.info.fontSize then labels may collide
     float fontSize = styleProperties.size;
     float fontScale = fontSize / sdfFontSize;
     matrix::scale(exMatrix, exMatrix, fontScale, fontScale, 1.0f);
 
+    // calculate how much longer the real world distance is at the top of the screen
+    // than at the middle of the screen.
+    float topedgelength = std::sqrt(std::pow(state.getHeight(), 2) / 4.0f * (1.0f + std::pow(state.getAltitude(), 2)));
+    float x = state.getHeight() / 2.0f * std::tan(state.getPitch());
+    float extra = (topedgelength + x) / topedgelength - 1;
+
     useProgram(sdfShader.program);
     sdfShader.u_matrix = vtxMatrix;
     sdfShader.u_exmatrix = exMatrix;
     sdfShader.u_texsize = texsize;
+    sdfShader.u_skewed = skewed;
+    sdfShader.u_extra = extra;
 
     // adjust min/max zooms for variable font sies
     float zoomAdjust = std::log(fontSize / bucketProperties.size) / std::log(2);
@@ -70,7 +85,7 @@ void Painter::renderSDF(SymbolBucket &bucket,
     // We're drawing in the translucent pass which is bottom-to-top, so we need
     // to draw the halo first.
     if (styleProperties.halo_color[3] > 0.0f && styleProperties.halo_width > 0.0f) {
-        sdfShader.u_gamma = styleProperties.halo_blur * blurOffset / fontScale / sdfPx + gamma;
+        sdfShader.u_gamma = (styleProperties.halo_blur * blurOffset / fontScale / sdfPx + gamma) * gammaScale;
 
         if (styleProperties.opacity < 1.0f) {
             Color color = styleProperties.halo_color;
@@ -91,7 +106,7 @@ void Painter::renderSDF(SymbolBucket &bucket,
 
     // Then, we draw the text/icon over the halo
     if (styleProperties.color[3] > 0.0f) {
-        sdfShader.u_gamma = gamma;
+        sdfShader.u_gamma = gamma * gammaScale;
 
         if (styleProperties.opacity < 1.0f) {
             Color color = styleProperties.color;
@@ -120,7 +135,6 @@ void Painter::renderSymbol(SymbolBucket &bucket, const StyleLayer &layer_desc, c
     const auto &properties = layer_desc.getProperties<SymbolProperties>();
     const auto &layout = bucket.layout;
 
-    config.depthTest = true;
     config.depthMask = GL_FALSE;
 
     if (bucket.hasCollisionBoxData()) {
@@ -150,6 +164,8 @@ void Painter::renderSymbol(SymbolBucket &bucket, const StyleLayer &layer_desc, c
     config.stencilTest = drawAcrossEdges ? false : true;
 
     if (bucket.hasIconData()) {
+        config.depthTest = layout.icon.rotation_alignment == RotationAlignmentType::Map;
+
         bool sdf = bucket.sdfIcons;
 
         const float angleOffset =
@@ -160,7 +176,8 @@ void Painter::renderSymbol(SymbolBucket &bucket, const StyleLayer &layer_desc, c
         const float fontSize = properties.icon.size;
         const float fontScale = fontSize / 1.0f;
 
-        spriteAtlas->bind(state.isChanging() || layout.placement == PlacementType::Line || angleOffset != 0 || fontScale != 1 || sdf);
+        spriteAtlas->bind(state.isChanging() || layout.placement == PlacementType::Line
+                || angleOffset != 0 || fontScale != 1 || sdf || state.getPitch() != 0);
 
         if (sdf) {
             renderSDF(bucket,
@@ -175,19 +192,33 @@ void Painter::renderSymbol(SymbolBucket &bucket, const StyleLayer &layer_desc, c
         } else {
             mat4 vtxMatrix = translatedMatrix(matrix, properties.icon.translate, id, properties.icon.translate_anchor);
 
+            bool skewed = layout.icon.rotation_alignment == RotationAlignmentType::Map;
             mat4 exMatrix;
-            matrix::copy(exMatrix, projMatrix);
-
-            if (angleOffset) {
-                matrix::rotate_z(exMatrix, exMatrix, angleOffset);
+            float s;
+
+            if (skewed) {
+                matrix::identity(exMatrix);
+                s = 4096.0f / util::tileSize / id.overscaling / std::pow(2, state.getZoom() - id.z);
+            } else {
+                exMatrix = extrudeMatrix;
+                s = state.getAltitude();
             }
+            matrix::scale(exMatrix, exMatrix, s, s, 1);
 
             matrix::scale(exMatrix, exMatrix, fontScale, fontScale, 1.0f);
 
+            // calculate how much longer the real world distance is at the top of the screen
+            // than at the middle of the screen.
+            float topedgelength = std::sqrt(std::pow(state.getHeight(), 2) / 4.0f * (1.0f + std::pow(state.getAltitude(), 2)));
+            float x = state.getHeight() / 2.0f * std::tan(state.getPitch());
+            float extra = (topedgelength + x) / topedgelength - 1;
+
             useProgram(iconShader->program);
             iconShader->u_matrix = vtxMatrix;
             iconShader->u_exmatrix = exMatrix;
             iconShader->u_texsize = {{ float(spriteAtlas->getWidth()) / 4.0f, float(spriteAtlas->getHeight()) / 4.0f }};
+            iconShader->u_skewed = skewed;
+            iconShader->u_extra = extra;
 
             // adjust min/max zooms for variable font sies
             float zoomAdjust = std::log(fontSize / layout.icon.size) / std::log(2);
@@ -205,6 +236,8 @@ void Painter::renderSymbol(SymbolBucket &bucket, const StyleLayer &layer_desc, c
     }
 
     if (bucket.hasTextData()) {
+        config.depthTest = layout.text.rotation_alignment == RotationAlignmentType::Map;
+
         glyphAtlas->bind();
 
         renderSDF(bucket,
diff --git a/src/mbgl/shader/icon.vertex.glsl b/src/mbgl/shader/icon.vertex.glsl
index 549570021d..3850e01ab7 100644
--- a/src/mbgl/shader/icon.vertex.glsl
+++ b/src/mbgl/shader/icon.vertex.glsl
@@ -14,6 +14,8 @@ uniform float u_minfadezoom;
 uniform float u_maxfadezoom;
 uniform float u_fadezoom;
 uniform float u_opacity;
+uniform bool u_skewed;
+uniform float u_extra;
 
 uniform vec2 u_texsize;
 
@@ -51,7 +53,15 @@ void main() {
     // if label has been faded out, clip it
     z += step(v_alpha, 0.0);
 
-    gl_Position = u_matrix * vec4(a_pos, 0, 1) + u_exmatrix * vec4(a_offset / 64.0, z, 0);
+    if (u_skewed) {
+        vec4 extrude = u_exmatrix * vec4(a_offset / 64.0, 0, 0);
+        gl_Position = u_matrix * vec4(a_pos + extrude.xy, 0, 1);
+        gl_Position.z += z * gl_Position.w;
+    } else {
+        vec4 extrude = u_exmatrix * vec4(a_offset / 64.0, z, 0);
+        gl_Position = u_matrix * vec4(a_pos, 0, 1) + extrude;
+    }
+
     v_tex = a_tex / u_texsize;
 
     v_alpha *= u_opacity;
diff --git a/src/mbgl/shader/icon_shader.hpp b/src/mbgl/shader/icon_shader.hpp
index b6156ae9a0..18b0fce37b 100644
--- a/src/mbgl/shader/icon_shader.hpp
+++ b/src/mbgl/shader/icon_shader.hpp
@@ -21,6 +21,8 @@ public:
     Uniform<float>                u_fadezoom    = {"u_fadezoom",    *this};
     Uniform<float>                u_opacity     = {"u_opacity",     *this};
     Uniform<std::array<float, 2>> u_texsize     = {"u_texsize",     *this};
+    Uniform<int32_t>              u_skewed      = {"u_skewed",      *this};
+    Uniform<float>                u_extra       = {"u_extra",       *this};
 
 private:
     int32_t a_pos = -1;
diff --git a/src/mbgl/shader/sdf.fragment.glsl b/src/mbgl/shader/sdf.fragment.glsl
index d72d61dab1..a77e959e53 100644
--- a/src/mbgl/shader/sdf.fragment.glsl
+++ b/src/mbgl/shader/sdf.fragment.glsl
@@ -5,9 +5,11 @@ uniform float u_gamma;
 
 varying vec2 v_tex;
 varying float v_alpha;
+varying float v_gamma_scale;
 
 void main() {
     float dist = texture2D(u_texture, v_tex).a;
-    float alpha = smoothstep(u_buffer - u_gamma, u_buffer + u_gamma, dist) * v_alpha;
+    float gamma = u_gamma * v_gamma_scale;
+    float alpha = smoothstep(u_buffer - gamma, u_buffer + gamma, dist) * v_alpha;
     gl_FragColor = u_color * alpha;
 }
diff --git a/src/mbgl/shader/sdf.vertex.glsl b/src/mbgl/shader/sdf.vertex.glsl
index 192459f9da..5d2e1ce249 100644
--- a/src/mbgl/shader/sdf.vertex.glsl
+++ b/src/mbgl/shader/sdf.vertex.glsl
@@ -13,11 +13,14 @@ uniform float u_fadedist;
 uniform float u_minfadezoom;
 uniform float u_maxfadezoom;
 uniform float u_fadezoom;
+uniform bool u_skewed;
+uniform float u_extra;
 
 uniform vec2 u_texsize;
 
 varying vec2 v_tex;
 varying float v_alpha;
+varying float v_gamma_scale;
 
 void main() {
     vec2 a_tex = a_data1.xy;
@@ -48,6 +51,19 @@ void main() {
     // if label has been faded out, clip it
     show *= (1.0 - step(v_alpha, 0.0));
 
-    gl_Position = u_matrix * vec4(a_pos, 0, 1) + u_exmatrix * vec4(a_offset * show / 64.0, 0, 0);
+    if (u_skewed) {
+        vec4 extrude = u_exmatrix * vec4(a_offset * show / 64.0, 0, 0);
+        gl_Position = u_matrix * vec4(a_pos + extrude.xy, 0, 1);
+    } else {
+        vec4 extrude = u_exmatrix * vec4(a_offset * show / 64.0, 0, 0);
+        gl_Position = u_matrix * vec4(a_pos, 0, 1) + extrude;
+    }
+
+    // position of y on the screen
+    float y = gl_Position.y / gl_Position.w;
+    // how much features are squished in all directions by the perspectiveness
+    float perspective_scale = 1.0 / (1.0 - y * u_extra);
+    v_gamma_scale = perspective_scale;
+
     v_tex = a_tex / u_texsize;
 }
diff --git a/src/mbgl/shader/sdf_shader.hpp b/src/mbgl/shader/sdf_shader.hpp
index 36dfa30d3e..181788ab16 100644
--- a/src/mbgl/shader/sdf_shader.hpp
+++ b/src/mbgl/shader/sdf_shader.hpp
@@ -23,6 +23,8 @@ public:
     Uniform<float>                u_minfadezoom = {"u_minfadezoom", *this};
     Uniform<float>                u_maxfadezoom = {"u_maxfadezoom", *this};
     Uniform<float>                u_fadezoom    = {"u_fadezoom",    *this};
+    Uniform<int32_t>              u_skewed      = {"u_skewed",      *this};
+    Uniform<float>                u_extra       = {"u_extra",       *this};
 
 protected:
     int32_t a_pos = -1;