87 lines
2.3 KiB
Bash
87 lines
2.3 KiB
Bash
/*
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* Copyright 2011-2023 Branimir Karadzic. All rights reserved.
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* License: https://github.com/bkaradzic/bgfx/blob/master/LICENSE
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*/
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/*
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* Reference(s):
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* - Based on Virtual Texture Demo by Brad Blanchard
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* http://web.archive.org/web/20190103162638/http://linedef.com/virtual-texture-demo.html
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*/
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uniform vec4 u_vt_settings_1;
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uniform vec4 u_vt_settings_2;
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#define VirtualTextureSize u_vt_settings_1.x
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#define AtlasScale u_vt_settings_1.y
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#define BorderScale u_vt_settings_1.z
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#define BorderOffset u_vt_settings_1.w
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#define MipBias u_vt_settings_2.x
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#define PageTableSize u_vt_settings_2.y
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SAMPLER2D(s_vt_page_table, 0);
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SAMPLER2D(s_vt_texture_atlas, 1);
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// This function estimates mipmap levels
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float MipLevel( vec2 uv, float size )
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{
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vec2 dx = dFdx( uv * size );
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vec2 dy = dFdy( uv * size );
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float d = max( dot( dx, dx ), dot( dy, dy ) );
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return max( 0.5 * log2( d ), 0 );
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}
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// This function samples the page table and returns the page's
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// position and mip level.
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vec3 SampleTable( vec2 uv, float mip )
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{
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vec2 offset = fract( uv * PageTableSize ) / PageTableSize;
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return texture2DLod( s_vt_page_table, uv - offset, mip ).xyz;
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}
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// This functions samples from the texture atlas and returns the final color
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vec4 SampleAtlas( vec3 page, vec2 uv )
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{
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float mipsize = exp2( floor( page.z * 255.0 + 0.5 ) );
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uv = fract( uv * PageTableSize / mipsize );
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uv *= BorderScale;
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uv += BorderOffset;
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vec2 offset = floor( page.xy * 255.0 + 0.5 );
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return texture2D( s_vt_texture_atlas, ( offset + uv ) * AtlasScale );
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}
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// Ugly brute force trilinear, look up twice and mix
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vec4 VirtualTextureTrilinear( vec2 uv )
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{
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float miplevel = MipLevel( uv, VirtualTextureSize );
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miplevel = clamp( miplevel, 0.0, log2( PageTableSize )-1.0 );
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float mip1 = floor( miplevel );
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float mip2 = mip1 + 1.0;
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float mipfrac = miplevel - mip1;
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vec3 page1 = SampleTable( uv, mip1 );
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vec3 page2 = SampleTable( uv, mip2 );
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vec4 sample1 = SampleAtlas( page1, uv );
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vec4 sample2 = SampleAtlas( page2, uv );
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return mix( sample1, sample2, mipfrac );
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}
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// Simple bilinear
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vec4 VirtualTexture( vec2 uv )
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{
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float mip = floor( MipLevel( uv, VirtualTextureSize ) );
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mip = clamp( mip, 0, log2( PageTableSize ) );
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vec3 page = SampleTable( uv, mip );
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return SampleAtlas( page, uv );
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}
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