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Fix Two Issues with the glsl Bilinear Shader

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1. Off-by-one pixel coordinates
2. Sampling of wrong pixels at some non-integer stretch factors

First was noticed while comparing screenshots of the software and opengl w/glsl renderers (opengl output was shifted up and to the right). Fixed by subtracting a 1/2 pixel from the texture coordinates when calculating the bottom left pixel to use for interpolation.

Second was apparent when running pac-man fullscreen on a 1920x1080 screen and allowing non-integer stretching. Manifested as irregular horizontal 'steps' in the output. Fixed by sampling from the center of all pixels which should avoid any funny business in regards to pixel coordinate rounding.
This commit is contained in:
Aaron 2017-12-29 20:37:44 -08:00
parent 1624208a65
commit 6c456a2865
2 changed files with 36 additions and 37 deletions
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10
src/osd/modules/opengl/shader/glsl_bilinear_rgb32_dir.fsh
View File

@ -13,8 +13,6 @@ uniform vec4 vid_attributes; // gamma, contrast, brightness
void main()
{
vec2 xy = gl_TexCoord[0].st;
// mix(x,y,a): x*(1-a) + y*a
//
// bilinear filtering includes 2 mix:
@ -25,9 +23,11 @@ void main()
//
// so we can use the build in mix function for these 2 computations ;-)
//
vec2 uv_ratio = fract(xy*color_texture_pow2_sz); // xy*color_texture_pow2_sz - floor(xy*color_texture_pow2_sz);
vec2 one = 1.0/color_texture_pow2_sz;
vec2 pixel = gl_TexCoord[0].st * color_texture_pow2_sz - 0.5;
vec2 uv_ratio = fract(pixel);
vec2 one = 1.0 / color_texture_pow2_sz;
vec2 xy = (floor(pixel) + 0.5) * one;
#if 1
vec4 col, col2;

63
src/osd/modules/opengl/shader/glsl_bilinear_rgb32_dir.fsh.c
View File

@ -1,7 +1,6 @@
// license:BSD-3-Clause
// copyright-holders:Sven Gothel
const char glsl_bilinear_rgb32_dir_fsh_src[] =
"\n"
"// license:BSD-3-Clause\n"
"// copyright-holders:Sven Gothel\n"
"#pragma optimize (on)\n"
"#pragma debug (off)\n"
"\n"
@ -15,43 +14,43 @@ const char glsl_bilinear_rgb32_dir_fsh_src[] =
"\n"
"void main()\n"
"{\n"
" vec2 xy = gl_TexCoord[0].st;\n"
"\n"
" // mix(x,y,a): x*(1-a) + y*a\n"
" //\n"
" // bilinear filtering includes 2 mix:\n"
" //\n"
" // pix1 = tex[x0][y0] * ( 1 - u_ratio ) + tex[x1][y0] * u_ratio\n"
" // pix2 = tex[x0][y1] * ( 1 - u_ratio ) + tex[x1][y1] * u_ratio\n"
" // fin = pix1 * ( 1 - v_ratio ) + pix2 * v_ratio\n"
" //\n"
" // so we can use the build in mix function for these 2 computations ;-)\n"
" //\n"
" vec2 uv_ratio = fract(xy*color_texture_pow2_sz); // xy*color_texture_pow2_sz - floor(xy*color_texture_pow2_sz);\n"
" vec2 one = 1.0/color_texture_pow2_sz;\n"
"\n"
" // mix(x,y,a): x*(1-a) + y*a\n"
" //\n"
" // bilinear filtering includes 2 mix:\n"
" //\n"
" // pix1 = tex[x0][y0] * ( 1 - u_ratio ) + tex[x1][y0] * u_ratio\n"
" // pix2 = tex[x0][y1] * ( 1 - u_ratio ) + tex[x1][y1] * u_ratio\n"
" // fin = pix1 * ( 1 - v_ratio ) + pix2 * v_ratio\n"
" //\n"
" // so we can use the build in mix function for these 2 computations ;-)\n"
" //\n"
" vec2 pixel = gl_TexCoord[0].st * color_texture_pow2_sz - 0.5;\n"
" vec2 uv_ratio = fract(pixel);\n"
" vec2 one = 1.0 / color_texture_pow2_sz;\n"
" vec2 xy = (floor(pixel) + 0.5) * one;\n"
" \n"
"#if 1\n"
" vec4 col, col2;\n"
" vec4 col, col2;\n"
"\n"
" col = mix( TEX2D(xy ), TEX2D(xy + vec2(one.x, 0.0)), uv_ratio.x);\n"
" col2 = mix( TEX2D(xy + vec2(0.0, one.y)), TEX2D(xy + one ), uv_ratio.x);\n"
" col = mix ( col, col2, uv_ratio.y );\n"
" col = mix( TEX2D(xy ), TEX2D(xy + vec2(one.x, 0.0)), uv_ratio.x);\n"
" col2 = mix( TEX2D(xy + vec2(0.0, one.y)), TEX2D(xy + one ), uv_ratio.x);\n"
" col = mix ( col, col2, uv_ratio.y );\n"
"#else\n"
" // doesn't work on MacOSX GLSL engine ..\n"
" //\n"
" vec4 col = mix ( mix( TEX2D(xy ), TEX2D(xy + vec2(one.x, 0.0)), uv_ratio.x),\n"
" mix( TEX2D(xy + vec2(0.0, one.y)), TEX2D(xy + one ), uv_ratio.x), uv_ratio.y );\n"
" // doesn't work on MacOSX GLSL engine ..\n"
" //\n"
" vec4 col = mix ( mix( TEX2D(xy ), TEX2D(xy + vec2(one.x, 0.0)), uv_ratio.x),\n"
" mix( TEX2D(xy + vec2(0.0, one.y)), TEX2D(xy + one ), uv_ratio.x), uv_ratio.y );\n"
"#endif\n"
"\n"
" // gamma, contrast, brightness equation from: rendutil.h / apply_brightness_contrast_gamma_fp\n"
" // gamma, contrast, brightness equation from: rendutil.h / apply_brightness_contrast_gamma_fp\n"
"\n"
"#ifdef DO_GAMMA\n"
" // gamma/contrast/brightness\n"
" vec4 gamma = vec4(1.0 / vid_attributes.r, 1.0 / vid_attributes.r, 1.0 / vid_attributes.r, 0.0);\n"
" gl_FragColor = ( pow ( col, gamma ) * vid_attributes.g) + vid_attributes.b - 1.0;\n"
" // gamma/contrast/brightness\n"
" vec4 gamma = vec4(1.0 / vid_attributes.r, 1.0 / vid_attributes.r, 1.0 / vid_attributes.r, 0.0);\n"
" gl_FragColor = ( pow ( col, gamma ) * vid_attributes.g) + vid_attributes.b - 1.0;\n"
"#else\n"
" // contrast/brightness\n"
" gl_FragColor = ( col * vid_attributes.g) + vid_attributes.b - 1.0;\n"
" // contrast/brightness\n"
" gl_FragColor = ( col * vid_attributes.g) + vid_attributes.b - 1.0;\n"
"#endif\n"
"}\n"
"\n"