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ba21fb947e
There are cases where alpha is multiplied unnecessarily. This change attempts to use premultiplied alpha blending for composition. To keep this change simple, The filter chain will continue to use straight alpha. Otherwise, every source would need to modified to output premultiplied, and every filter modified for premultiplied input. "DrawAlphaDivide" shader techniques have been added to convert from premultiplied alpha to straight alpha for final output. "DrawMatrix" techniques ignore alpha, so they do not appear to need changing. One remaining issue is that scale effects are set up here to use the same shader logic for both scale filters (straight alpha - incorrectly), and output composition (premultiplied alpha - correctly). A fix could be made to add additional shaders for straight alpha, but the "real" fix may be to eliminate the straight alpha path at some point. For graphics, SrcBlendAlpha and DestBlendAlpha were both ONE, and could combine together to form alpha values greater than one. This is not as noticeable of a problem for UNORM targets because the channels are clamped, but it will likely become a problem in more situations if FLOAT targets are used. This change switches DestBlendAlpha to INVSRCALPHA. The blending behavior of stacked transparents is preserved without overflowing the alpha channel. obs-transitions: Use premultiplied alpha blend, and simplify shaders because both inputs and outputs use premultiplied alpha now. Fixes https://obsproject.com/mantis/view.php?id=1108
40 lines
717 B
Plaintext
40 lines
717 B
Plaintext
uniform float4x4 ViewProj;
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uniform texture2d tex_a;
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uniform texture2d tex_b;
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uniform float fade_val;
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sampler_state textureSampler {
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Filter = Linear;
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AddressU = Clamp;
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AddressV = Clamp;
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};
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struct VertData {
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float4 pos : POSITION;
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float2 uv : TEXCOORD0;
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};
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VertData VSDefault(VertData v_in)
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{
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VertData vert_out;
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vert_out.pos = mul(float4(v_in.pos.xyz, 1.0), ViewProj);
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vert_out.uv = v_in.uv;
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return vert_out;
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}
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float4 PSFade(VertData v_in) : TARGET
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{
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float4 a_val = tex_a.Sample(textureSampler, v_in.uv);
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float4 b_val = tex_b.Sample(textureSampler, v_in.uv);
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return lerp(a_val, b_val, fade_val);
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}
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technique Fade
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{
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pass
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{
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vertex_shader = VSDefault(v_in);
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pixel_shader = PSFade(v_in);
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}
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}
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