improve dashed and patterned line antialiasing

in perspective view. This is exactly the same approach used for regular
lines. I just forgot to implement it for these types of lines.

src/mbgl/renderer/painter_line.cpp

@@ -97,6 +97,8 @@ void Painter::renderLine(LineBucket& bucket, const StyleLayer &layer_desc, const
         linesdfShader->u_image = 0;
         linesdfShader->u_sdfgamma = lineAtlas->width / (properties.dash_line_width * std::min(posA.width, posB.width) * 256.0 * data.pixelRatio) / 2;
         linesdfShader->u_mix = properties.dash_array.t;
+        linesdfShader->u_extra = extra;
+        linesdfShader->u_antialiasingmatrix = antialiasingMatrix;
 
         bucket.drawLineSDF(*linesdfShader);
 
@@ -122,6 +124,8 @@ void Painter::renderLine(LineBucket& bucket, const StyleLayer &layer_desc, const
         linepatternShader->u_pattern_br_b = imagePosB.br;
         linepatternShader->u_fade = properties.image.t;
         linepatternShader->u_opacity = properties.opacity;
+        linepatternShader->u_extra = extra;
+        linepatternShader->u_antialiasingmatrix = antialiasingMatrix;
 
         MBGL_CHECK_ERROR(glActiveTexture(GL_TEXTURE0));
         spriteAtlas->bind(true);

src/mbgl/shader/line.vertex.glsl

@@ -34,13 +34,13 @@ void main() {
 
     // Scale the extrusion vector down to a normal and then up by the line width
     // of this vertex.
-    vec4 dist = vec4(u_linewidth.s * a_extrude * scale, 0.0, 0.0);
+    vec2 dist = u_linewidth.s * a_extrude * scale;
 
     // Remove the texture normal bit of the position before scaling it with the
     // model/view matrix. Add the extrusion vector *after* the model/view matrix
     // because we're extruding the line in pixel space, regardless of the current
     // tile's zoom level.
-    gl_Position = u_matrix * vec4(floor(a_pos * 0.5) + dist.xy / u_ratio, 0.0, 1.0);
+    gl_Position = u_matrix * vec4(floor(a_pos * 0.5) + dist / u_ratio, 0.0, 1.0);
 
     // position of y on the screen
     float y = gl_Position.y / gl_Position.w;

src/mbgl/shader/linepattern.fragment.glsl

@@ -1,5 +1,4 @@
 uniform vec2 u_linewidth;
-uniform float u_point;
 uniform float u_blur;
 
 uniform vec2 u_pattern_size_a;
@@ -15,17 +14,17 @@ uniform sampler2D u_image;
 
 varying vec2 v_normal;
 varying float v_linesofar;
+varying float v_gamma_scale;
 
 void main() {
     // Calculate the distance of the pixel from the line in pixels.
-    float dist = length(v_normal) * (1.0 - u_point) + u_point * length(gl_PointCoord * 2.0 - 1.0);
-
-    dist *= u_linewidth.s;
+    float dist = length(v_normal) * u_linewidth.s;
 
     // Calculate the antialiasing fade factor. This is either when fading in
     // the line in case of an offset line (v_linewidth.t) or when fading out
     // (v_linewidth.s)
-    float alpha = clamp(min(dist - (u_linewidth.t - u_blur), u_linewidth.s - dist) / u_blur, 0.0, 1.0);
+    float blur = u_blur * v_gamma_scale;
+    float alpha = clamp(min(dist - (u_linewidth.t - blur), u_linewidth.s - dist) / blur, 0.0, 1.0);
 
     float x_a = mod(v_linesofar / u_pattern_size_a.x, 1.0);
     float y_a = 0.5 + (v_normal.y * u_linewidth.s / u_pattern_size_a.y);

src/mbgl/shader/linepattern.vertex.glsl

@@ -18,10 +18,13 @@ uniform mat4 u_exmatrix;
 uniform float u_ratio;
 uniform vec2 u_linewidth;
 uniform vec4 u_color;
-uniform float u_point;
+
+uniform float u_extra;
+uniform mat2 u_antialiasingmatrix;
 
 varying vec2 v_normal;
 varying float v_linesofar;
+varying float v_gamma_scale;
 
 void main() {
     vec2 a_extrude = a_data.xy;
@@ -37,24 +40,23 @@ void main() {
 
     // Scale the extrusion vector down to a normal and then up by the line width
     // of this vertex.
-    vec2 extrude = a_extrude * scale;
-    vec2 dist = u_linewidth.s * extrude * (1.0 - u_point);
-
-    // If the x coordinate is the maximum integer, we move the z coordinates out
-    // of the view plane so that the triangle gets clipped. This makes it easier
-    // for us to create degenerate triangle strips.
-    float z = step(32767.0, a_pos.x);
-
-    // When drawing points, skip every other vertex
-    z += u_point * step(1.0, v_normal.y);
+    vec2 dist = u_linewidth.s * a_extrude * scale;
 
     // Remove the texture normal bit of the position before scaling it with the
     // model/view matrix. Add the extrusion vector *after* the model/view matrix
     // because we're extruding the line in pixel space, regardless of the current
     // tile's zoom level.
     gl_Position = u_matrix * vec4(floor(a_pos / 2.0) + dist.xy / u_ratio, 0.0, 1.0);
-    v_linesofar = a_linesofar;// * u_ratio;
+    v_linesofar = a_linesofar;
 
+    // position of y on the screen
+    float y = gl_Position.y / gl_Position.w;
 
-    gl_PointSize = 2.0 * u_linewidth.s - 1.0;
+    // how much features are squished in the y direction by the tilt
+    float squish_scale = length(a_extrude) / length(u_antialiasingmatrix * a_extrude);
+
+    // 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 * squish_scale;
 }

src/mbgl/shader/linepattern_shader.hpp

@@ -26,6 +26,8 @@ public:
     Uniform<float>                u_blur         = {"u_blur",         *this};
     Uniform<float>                u_fade         = {"u_fade",         *this};
     Uniform<float>                u_opacity      = {"u_opacity",      *this};
+    Uniform<float>                 u_extra     = {"u_extra",     *this};
+    UniformMatrix<2>               u_antialiasingmatrix  = {"u_antialiasingmatrix",  *this};
 
 private:
     int32_t a_pos = -1;

src/mbgl/shader/linesdf.fragment.glsl

@@ -8,6 +8,7 @@ uniform float u_mix;
 varying vec2 v_normal;
 varying vec2 v_tex_a;
 varying vec2 v_tex_b;
+varying float v_gamma_scale;
 
 void main() {
     // Calculate the distance of the pixel from the line in pixels.
@@ -16,7 +17,8 @@ void main() {
     // Calculate the antialiasing fade factor. This is either when fading in
     // the line in case of an offset line (v_linewidth.t) or when fading out
     // (v_linewidth.s)
-    float alpha = clamp(min(dist - (u_linewidth.t - u_blur), u_linewidth.s - dist) / u_blur, 0.0, 1.0);
+    float blur = u_blur * v_gamma_scale;
+    float alpha = clamp(min(dist - (u_linewidth.t - blur), u_linewidth.s - dist) / blur, 0.0, 1.0);
 
     float sdfdist_a = texture2D(u_image, v_tex_a).a;
     float sdfdist_b = texture2D(u_image, v_tex_b).a;

src/mbgl/shader/linesdf.vertex.glsl

@@ -22,9 +22,13 @@ uniform float u_tex_y_a;
 uniform vec2 u_patternscale_b;
 uniform float u_tex_y_b;
 
+uniform float u_extra;
+uniform mat2 u_antialiasingmatrix;
+
 varying vec2 v_normal;
 varying vec2 v_tex_a;
 varying vec2 v_tex_b;
+varying float v_gamma_scale;
 
 void main() {
     vec2 a_extrude = a_data.xy;
@@ -40,14 +44,25 @@ void main() {
 
     // Scale the extrusion vector down to a normal and then up by the line width
     // of this vertex.
-    vec4 dist = vec4(u_linewidth.s * a_extrude * scale, 0.0, 0.0);
+    vec2 dist = u_linewidth.s * a_extrude * scale;
 
     // Remove the texture normal bit of the position before scaling it with the
     // model/view matrix. Add the extrusion vector *after* the model/view matrix
     // because we're extruding the line in pixel space, regardless of the current
     // tile's zoom level.
-    gl_Position = u_matrix * vec4(floor(a_pos * 0.5) + dist.xy / u_ratio, 0.0, 1.0);
+    gl_Position = u_matrix * vec4(floor(a_pos * 0.5) + dist / u_ratio, 0.0, 1.0);
 
     v_tex_a = vec2(a_linesofar * u_patternscale_a.x, normal.y * u_patternscale_a.y + u_tex_y_a);
     v_tex_b = vec2(a_linesofar * u_patternscale_b.x, normal.y * u_patternscale_b.y + u_tex_y_b);
+
+    // position of y on the screen
+    float y = gl_Position.y / gl_Position.w;
+
+    // how much features are squished in the y direction by the tilt
+    float squish_scale = length(a_extrude) / length(u_antialiasingmatrix * a_extrude);
+
+    // how much features are squished in all directions by the perspectiveness
+    float perspective_scale = 1.0 / (1.0 - min(y * u_extra, 0.9));
+
+    v_gamma_scale = perspective_scale * squish_scale;
 }

src/mbgl/shader/linesdf_shader.hpp

@@ -25,6 +25,8 @@ public:
     Uniform<int32_t>               u_image     = {"u_image",     *this};
     Uniform<float>                 u_sdfgamma  = {"u_sdfgamma",  *this};
     Uniform<float>                 u_mix       = {"u_mix",       *this};
+    Uniform<float>                 u_extra     = {"u_extra",     *this};
+    UniformMatrix<2>               u_antialiasingmatrix  = {"u_antialiasingmatrix",  *this};
 
 private:
     int32_t a_pos = -1;