need to update sdl

external/SDL/test/testgpurender_msdf.frag.hlsl

@@ -1,37 +0,0 @@
-cbuffer Context : register(b0, space3) {
-    float distance_field_range;
-    float2 texture_size;
-};
-
-Texture2D u_texture : register(t0, space2);
-SamplerState u_sampler : register(s0, space2);
-
-struct PSInput {
-    float4 v_color : COLOR0;
-    float2 v_uv : TEXCOORD0;
-};
-
-struct PSOutput {
-    float4 o_color : SV_Target;
-};
-
-float median(float r, float g, float b) {
-    return max(min(r, g), min(max(r, g), b));
-}
-
-float screenPxRange(float2 texCoord) {
-    float2 unitRange = float2(distance_field_range, distance_field_range)/texture_size;
-    float2 screenTexSize = float2(1.0, 1.0)/fwidth(texCoord);
-    return max(0.5*dot(unitRange, screenTexSize), 1.0);
-}
-
-PSOutput main(PSInput input) {
-    PSOutput output;
-    float3 msd = u_texture.Sample(u_sampler, input.v_uv).rgb;
-    float sd = median(msd.r, msd.g, msd.b);
-    float screenPxDistance = screenPxRange(input.v_uv)*(sd - 0.5);
-    float opacity = clamp(screenPxDistance + 0.5, 0.0, 1.0);
-    output.o_color.rgb = input.v_color.rgb;
-    output.o_color.a = (input.v_color.a * opacity);
-    return output;
-}