Pack min + max into one attribute :muscle:

Some devices supported by Mapbox GL provide only 8 vertex attributes; this change packs existing attributes to get us just under that limit.

For properties using a composite function, pack the min and max values into a single attribute with two logical components instead of using two separate attributes and buffers. Special logic is included for color attributes, whose integer components must be packed into the available bits of floating-point attributes. (We don't have access to ivec types in GL ES 2.0.)

For source functions, continue to bind just a one-component attribute even though the GLSL type is vec2 (or vec4 for colors). The type-checking done by gl::Attribute is relaxed slightly to accommodate this.

1 files changed, 4 insertions, 6 deletions

diff --git a/src/mbgl/shaders/fill.cpp b/src/mbgl/shaders/fill.cpp
index d0fc3a7033..a1fba4d749 100644
--- a/src/mbgl/shaders/fill.cpp
+++ b/src/mbgl/shaders/fill.cpp
@@ -12,17 +12,15 @@ attribute vec2 a_pos;
 uniform mat4 u_matrix;
 
 uniform lowp float a_color_t;
-attribute lowp vec4 a_color_min;
-attribute lowp vec4 a_color_max;
+attribute lowp vec4 a_color;
 varying lowp vec4 color;
 uniform lowp float a_opacity_t;
-attribute lowp float a_opacity_min;
-attribute lowp float a_opacity_max;
+attribute lowp vec2 a_opacity;
 varying lowp float opacity;
 
 void main() {
-    color = mix(a_color_min, a_color_max, a_color_t);
-    opacity = mix(a_opacity_min, a_opacity_max, a_opacity_t);
+    color = unpack_mix_vec4(a_color, a_color_t);
+    opacity = unpack_mix_vec2(a_opacity, a_opacity_t);
 
     gl_Position = u_matrix * vec4(a_pos, 0, 1);
 }