samples: core: fix sampler type

samples/core/shaders/default.shader

@@ -352,7 +352,7 @@ bgfx_shaders = {
 		"""
 
 		fs_code = """
-			ISAMPLER2D(s_selection, 0);
+			USAMPLER2D(s_selection, 0);
 			SAMPLER2D(s_selection_depth, 1);
 			SAMPLER2D(s_main_depth, 2);
 			uniform vec4 u_outline_color;
@@ -361,7 +361,7 @@ bgfx_shaders = {
 			{
 				vec2 tex_size = textureSize(s_selection, 0) - vec2(1, 1);
 
-				int id[8];
+				uint id[8];
 				id[0] = texelFetch(s_selection, ivec2(v_texcoord0 * tex_size + vec2(-1, -1)), 0).r;
 				id[1] = texelFetch(s_selection, ivec2(v_texcoord0 * tex_size + vec2( 0, -1)), 0).r;
 				id[2] = texelFetch(s_selection, ivec2(v_texcoord0 * tex_size + vec2( 1, -1)), 0).r;
@@ -371,7 +371,7 @@ bgfx_shaders = {
 				id[6] = texelFetch(s_selection, ivec2(v_texcoord0 * tex_size + vec2(-1,  1)), 0).r;
 				id[7] = texelFetch(s_selection, ivec2(v_texcoord0 * tex_size + vec2(-1,  0)), 0).r;
 
-				int ref_id = texelFetch(s_selection, ivec2(v_texcoord0 * tex_size), 0).r;
+				uint ref_id = texelFetch(s_selection, ivec2(v_texcoord0 * tex_size), 0).r;
 
 				float alpha = 0.0;
 				for (int ii = 0; ii < 8; ++ii)