Merge pull request #15 from mapbox/unskew

text-pitch-alignment

src/icon.vertex.glsl

@@ -16,7 +16,7 @@ attribute vec4 a_data2;
 uniform mat4 u_matrix;
 
 uniform mediump float u_zoom;
-uniform bool u_skewed;
+uniform bool u_rotate_with_map;
 uniform vec2 u_extrude_scale;
 
 uniform vec2 u_texsize;
@@ -35,7 +35,7 @@ void main() {
     mediump float z = 2.0 - step(a_minzoom, u_zoom) - (1.0 - step(a_maxzoom, u_zoom));
 
     vec2 extrude = u_extrude_scale * (a_offset / 64.0);
-    if (u_skewed) {
+    if (u_rotate_with_map) {
         gl_Position = u_matrix * vec4(a_pos + extrude, 0, 1);
         gl_Position.z += z * gl_Position.w;
     } else {

src/sdf.vertex.glsl

@@ -6,6 +6,8 @@ precision highp float;
 #define highp
 #endif
 
+const float PI = 3.141592653589793;
+
 attribute vec2 a_pos;
 attribute vec2 a_offset;
 attribute vec4 a_data1;
@@ -16,7 +18,11 @@ attribute vec4 a_data2;
 uniform mat4 u_matrix;
 
 uniform mediump float u_zoom;
-uniform bool u_skewed;
+uniform bool u_rotate_with_map;
+uniform bool u_pitch_with_map;
+uniform mediump float u_pitch;
+uniform mediump float u_bearing;
+uniform mediump float u_aspect_ratio;
 uniform vec2 u_extrude_scale;
 
 uniform vec2 u_texsize;
@@ -35,11 +41,45 @@ void main() {
     // u_zoom is the current zoom level adjusted for the change in font size
     mediump float z = 2.0 - step(a_minzoom, u_zoom) - (1.0 - step(a_maxzoom, u_zoom));
 
-    vec2 extrude = u_extrude_scale * (a_offset / 64.0);
-    if (u_skewed) {
+    // pitch-alignment: map
+    // rotation-alignment: map | viewport
+    if (u_pitch_with_map) {
+        lowp float angle = u_rotate_with_map ? (a_data1[3] / 256.0 * 2.0 * PI) : u_bearing;
+        lowp float asin = sin(angle);
+        lowp float acos = cos(angle);
+        mat2 RotationMatrix = mat2(acos, asin, -1.0 * asin, acos);
+        vec2 offset = RotationMatrix * a_offset;
+        vec2 extrude = u_extrude_scale * (offset / 64.0);
         gl_Position = u_matrix * vec4(a_pos + extrude, 0, 1);
         gl_Position.z += z * gl_Position.w;
+    // pitch-alignment: viewport
+    // rotation-alignment: map
+    } else if (u_rotate_with_map) {
+        // foreshortening factor to apply on pitched maps
+        // as a label goes from horizontal <=> vertical in angle
+        // it goes from 0% foreshortening to up to around 70% foreshortening
+        lowp float pitchfactor = 1.0 - cos(u_pitch * sin(u_pitch * 0.75));
+
+        lowp float lineangle = a_data1[3] / 256.0 * 2.0 * PI;
+
+        // use the lineangle to position points a,b along the line
+        // project the points and calculate the label angle in projected space
+        // this calculation allows labels to be rendered unskewed on pitched maps
+        vec4 a = u_matrix * vec4(a_pos, 0, 1);
+        vec4 b = u_matrix * vec4(a_pos + vec2(cos(lineangle),sin(lineangle)), 0, 1);
+        lowp float angle = atan((b[1]/b[3] - a[1]/a[3])/u_aspect_ratio, b[0]/b[3] - a[0]/a[3]);
+        lowp float asin = sin(angle);
+        lowp float acos = cos(angle);
+        mat2 RotationMatrix = mat2(acos, -1.0 * asin, asin, acos);
+
+        vec2 offset = RotationMatrix * (vec2((1.0-pitchfactor)+(pitchfactor*cos(angle*2.0)), 1.0) * a_offset);
+        vec2 extrude = u_extrude_scale * (offset / 64.0);
+        gl_Position = u_matrix * vec4(a_pos, 0, 1) + vec4(extrude, 0, 0);
+        gl_Position.z += z * gl_Position.w;
+    // pitch-alignment: viewport
+    // rotation-alignment: viewport
     } else {
+        vec2 extrude = u_extrude_scale * (a_offset / 64.0);
         gl_Position = u_matrix * vec4(a_pos, 0, 1) + vec4(extrude, 0, 0);
     }