Fix shader compilation under Android

engine/gui/Gui.cpp

@@ -60,6 +60,7 @@ GPUProgramId		font_program;
 UniformId			font_uniform;
 
 static const char* default_vertex =
+	"precision mediump float;"
 	"uniform mat4      	u_model_view_projection;"
 
 	"attribute vec4    	a_position;"
@@ -77,6 +78,7 @@ static const char* default_vertex =
 	"}";
 
 static const char* default_fragment =
+	"precision mediump float;"
 	"varying vec4            color;"
 
 	"void main(void)"
@@ -85,6 +87,7 @@ static const char* default_fragment =
 	"}";
 
 static const char* texture_fragment = 
+	"precision mediump float;"
 	"varying vec2       tex_coord0;"
 	"varying vec4       color;"
 
@@ -96,6 +99,7 @@ static const char* texture_fragment =
 	"}";
 
 static const char* sdf_vertex =
+	"precision mediump float;"
 	"uniform mat4      	u_model_view_projection;"
 
 	"attribute vec4		a_position;"
@@ -112,6 +116,7 @@ static const char* sdf_vertex =
 	"}";
 
 static const char* sdf_fragment =
+	"precision mediump float;"
 	"uniform sampler2D u_texture;"
 
 	"varying vec4 v_color;"

engine/renderers/RenderWorld.cpp

@@ -54,6 +54,7 @@ UniformId				u_lightmap_0;
 UniformId				u_brightness;
 
 static const char* default_vertex =
+	"precision mediump float;"
 	"uniform mat4      	u_model;"
 	"uniform mat4      	u_model_view_projection;"
 
@@ -72,12 +73,14 @@ static const char* default_vertex =
 	"}";
 
 static const char* default_fragment = 
+	"precision mediump float;"
 	"void main(void)"
 	"{"
 	"	gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);"
 	"}";
 
 static const char* texture_fragment = 
+	"precision mediump float;"
 	"varying vec2       tex_coord0;"
 	"varying vec4       color;"