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, 14 insertions, 21 deletions

diff --git a/src/mbgl/shaders/circle.cpp b/src/mbgl/shaders/circle.cpp
index 4b2bb7cecf..b479f1d40c 100644
--- a/src/mbgl/shaders/circle.cpp
+++ b/src/mbgl/shaders/circle.cpp
@@ -14,45 +14,38 @@ uniform vec2 u_extrude_scale;
 attribute vec2 a_pos;
 
 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_radius_t;
-attribute mediump float a_radius_min;
-attribute mediump float a_radius_max;
+attribute mediump vec2 a_radius;
 varying mediump float radius;
 uniform lowp float a_blur_t;
-attribute lowp float a_blur_min;
-attribute lowp float a_blur_max;
+attribute lowp vec2 a_blur;
 varying lowp float blur;
 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;
 uniform lowp float a_stroke_color_t;
-attribute lowp vec4 a_stroke_color_min;
-attribute lowp vec4 a_stroke_color_max;
+attribute lowp vec4 a_stroke_color;
 varying lowp vec4 stroke_color;
 uniform lowp float a_stroke_width_t;
-attribute mediump float a_stroke_width_min;
-attribute mediump float a_stroke_width_max;
+attribute mediump vec2 a_stroke_width;
 varying mediump float stroke_width;
 uniform lowp float a_stroke_opacity_t;
-attribute lowp float a_stroke_opacity_min;
-attribute lowp float a_stroke_opacity_max;
+attribute lowp vec2 a_stroke_opacity;
 varying lowp float stroke_opacity;
 
 varying vec2 v_extrude;
 varying lowp float v_antialiasblur;
 
 void main(void) {
-    color = mix(a_color_min, a_color_max, a_color_t);
-    radius = mix(a_radius_min, a_radius_max, a_radius_t);
-    blur = mix(a_blur_min, a_blur_max, a_blur_t);
-    opacity = mix(a_opacity_min, a_opacity_max, a_opacity_t);
-    stroke_color = mix(a_stroke_color_min, a_stroke_color_max, a_stroke_color_t);
-    stroke_width = mix(a_stroke_width_min, a_stroke_width_max, a_stroke_width_t);
-    stroke_opacity = mix(a_stroke_opacity_min, a_stroke_opacity_max, a_stroke_opacity_t);
+    color = unpack_mix_vec4(a_color, a_color_t);
+    radius = unpack_mix_vec2(a_radius, a_radius_t);
+    blur = unpack_mix_vec2(a_blur, a_blur_t);
+    opacity = unpack_mix_vec2(a_opacity, a_opacity_t);
+    stroke_color = unpack_mix_vec4(a_stroke_color, a_stroke_color_t);
+    stroke_width = unpack_mix_vec2(a_stroke_width, a_stroke_width_t);
+    stroke_opacity = unpack_mix_vec2(a_stroke_opacity, a_stroke_opacity_t);
 
     // unencode the extrusion vector that we snuck into the a_pos vector
     v_extrude = vec2(mod(a_pos, 2.0) * 2.0 - 1.0);