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added workaround to prevent clipped vertices from generating additional 

junk vertices
This commit is contained in:
Anthony Pesch 2017-11-16 19:54:03 -05:00
parent 7a2d89adfb
commit f177f6d40c
1 changed files with 19 additions and 6 deletions
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25
src/render/ta.glsl
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@ -15,14 +15,28 @@ static const char *ta_vp =
" var_offset_color = attr_offset_color;\n"
" var_texcoord = attr_texcoord;\n"
" // the z coordinate is actually 1/w, convert to w. note, there is no\n"
" // actual z coordinate provided to the ta, just this\n"
" highp float w = 1.0 / attr_xyz.z;\n"
" // if w is negative, this vertex will always fail the clip test which is\n"
" // defined as: -w <= z <= w\n"
" // however, since OpenGL tries to maintain connectivity when a polygon is\n"
" // clipped, a lot of junk vertices are generated. the best workaround so\n"
" // far is to force xyz=0 to avoid generating visible junk vertices\n"
" if (w < 0.0) {\n"
" gl_Position = vec4(0.0, 0.0, 0.0, w);\n"
" return;\n"
" }\n"
" // scale x from [0,640] -> [-1,1] and y from [0,480] to [-1,1]\n"
" gl_Position.xy = attr_xyz.xy * u_video_scale.xz + u_video_scale.yw;\n"
" // the z coordinate is actually 1/w, convert to w. note, there is no\n"
" // actual z coordinate provided to the ta, just 1/w. due to this, we set\n"
" // z = w in the vertex shader such that the clip test always passes, and\n"
" // then gl_FragDepth is manually set to w in the fragment shader\n"
" gl_Position.zw = 1.0f / attr_xyz.zz;\n"
" // since there isn't an actual z, set z = w to make the clip test always\n"
" // pass. because of this, after perspective division the fragment shader\n"
" // will always get a constant 1.0 for z, requiring it to explicitly set\n"
" // gl_FragDepth using the w component\n"
" gl_Position.zw = vec2(w, w);\n"
" // cancel the perspective divide on the xy, they're already in ndc space\n"
" gl_Position.xy *= gl_Position.w;\n"
@ -95,7 +109,6 @@ static const char *ta_fp =
" // note, 2^17 was chosen as ~100000 was largest value i'd seen passed as\n"
" // the w component at the time this was written\n"
" highp float w = 1.0 / gl_FragCoord.w;\n"
" gl_FragDepth = log2(1.0 + w) / 17.0;\n"