implement functions for patterns

It introduces a new function type, FadedStopsFunction, that transitions
between the stops values instead of interpolating between them.

3 files changed, 22 insertions, 13 deletions

diff --git a/src/mbgl/shader/pattern.fragment.glsl b/src/mbgl/shader/pattern.fragment.glsl
index ba6aed3023..a28a52ce36 100644
--- a/src/mbgl/shader/pattern.fragment.glsl
+++ b/src/mbgl/shader/pattern.fragment.glsl
@@ -1,20 +1,23 @@
 uniform float u_opacity;
-uniform vec2 u_pattern_tl;
-uniform vec2 u_pattern_br;
+uniform vec2 u_pattern_tl_a;
+uniform vec2 u_pattern_br_a;
+uniform vec2 u_pattern_tl_b;
+uniform vec2 u_pattern_br_b;
 uniform float u_mix;
 
 uniform sampler2D u_image;
 
-varying vec2 v_pos;
+varying vec2 v_pos_a;
+varying vec2 v_pos_b;
 
 void main() {
 
-    vec2 imagecoord = mod(v_pos, 1.0);
-    vec2 pos = mix(u_pattern_tl, u_pattern_br, imagecoord);
+    vec2 imagecoord = mod(v_pos_a, 1.0);
+    vec2 pos = mix(u_pattern_tl_a, u_pattern_br_a, imagecoord);
     vec4 color1 = texture2D(u_image, pos);
 
-    vec2 imagecoord2 = mod(imagecoord * 2.0, 1.0);
-    vec2 pos2 = mix(u_pattern_tl, u_pattern_br, imagecoord2);
+    vec2 imagecoord_b = mod(v_pos_b, 1.0);
+    vec2 pos2 = mix(u_pattern_tl_b, u_pattern_br_b, imagecoord_b);
     vec4 color2 = texture2D(u_image, pos2);
 
     gl_FragColor = mix(color1, color2, u_mix) * u_opacity;
diff --git a/src/mbgl/shader/pattern.vertex.glsl b/src/mbgl/shader/pattern.vertex.glsl
index f2de884ead..dff4469d2b 100644
--- a/src/mbgl/shader/pattern.vertex.glsl
+++ b/src/mbgl/shader/pattern.vertex.glsl
@@ -1,11 +1,14 @@
 uniform mat4 u_matrix;
-uniform mat3 u_patternmatrix;
+uniform mat3 u_patternmatrix_a;
+uniform mat3 u_patternmatrix_b;
 
 attribute vec2 a_pos;
 
-varying vec2 v_pos;
+varying vec2 v_pos_a;
+varying vec2 v_pos_b;
 
 void main() {
     gl_Position = u_matrix * vec4(a_pos, 0, 1);
-    v_pos = (u_patternmatrix * vec3(a_pos, 1)).xy;
+    v_pos_a = (u_patternmatrix_a * vec3(a_pos, 1)).xy;
+    v_pos_b = (u_patternmatrix_b * vec3(a_pos, 1)).xy;
 }
diff --git a/src/mbgl/shader/pattern_shader.hpp b/src/mbgl/shader/pattern_shader.hpp
index 9fabd8e18a..9fc8dcfa01 100644
--- a/src/mbgl/shader/pattern_shader.hpp
+++ b/src/mbgl/shader/pattern_shader.hpp
@@ -13,12 +13,15 @@ public:
     void bind(char *offset);
 
     UniformMatrix<4>              u_matrix        = {"u_matrix",        *this};
-    Uniform<std::array<float, 2>> u_pattern_tl    = {"u_pattern_tl",    *this};
-    Uniform<std::array<float, 2>> u_pattern_br    = {"u_pattern_br",    *this};
+    Uniform<std::array<float, 2>> u_pattern_tl_a    = {"u_pattern_tl_a",    *this};
+    Uniform<std::array<float, 2>> u_pattern_br_a    = {"u_pattern_br_a",    *this};
+    Uniform<std::array<float, 2>> u_pattern_tl_b    = {"u_pattern_tl_b",    *this};
+    Uniform<std::array<float, 2>> u_pattern_br_b    = {"u_pattern_br_b",    *this};
     Uniform<float>                u_opacity       = {"u_opacity",       *this};
     Uniform<float>                u_mix           = {"u_mix",           *this};
     Uniform<int32_t>              u_image         = {"u_image",         *this};
-    UniformMatrix<3>              u_patternmatrix = {"u_patternmatrix", *this};
+    UniformMatrix<3>              u_patternmatrix_a = {"u_patternmatrix_a", *this};
+    UniformMatrix<3>              u_patternmatrix_b = {"u_patternmatrix_b", *this};
 
 private:
     int32_t a_pos = -1;