Improve quality of YUVY and UYVY rendering

Idea is to upload YUYV/UYVY data as 2 textures and use GL_LINEAR like
in biplanar formats. Having proper interpolation of only one texture
(using e.g. mix function) resulted in vertical and horizontal 1 pixel
stripes depending on scale. The reason was float precision and
unexpected value of fract function. Additionally branching in shader
is expensive so this solution should be more performant.

Task-number: QTBUG-62155
Change-Id: I7ceeb09b4a54eecd16640a626b499d638b52c127
Reviewed-by: Christian Stromme <christian.stromme@qt.io>

2 files changed, 8 insertions, 28 deletions

diff --git a/src/qtmultimediaquicktools/shaders/uyvyvideo.frag b/src/qtmultimediaquicktools/shaders/uyvyvideo.frag
index 905035703..5c62441c2 100644
--- a/src/qtmultimediaquicktools/shaders/uyvyvideo.frag
+++ b/src/qtmultimediaquicktools/shaders/uyvyvideo.frag
@@ -1,22 +1,12 @@
-uniform sampler2D yuvTexture; // UYVY macropixel texture passed as RGBA format
-uniform mediump float imageWidth; // The UYVY texture appears to the shader with 1/2 the image width since we use the RGBA format to pass UYVY
+uniform sampler2D yTexture; // Y component passed as GL_LUMINANCE_ALPHA, in uyvy Y = a
+uniform sampler2D uvTexture; // UV component passed as RGBA macropixel, in uyvy U = r, V = b
 uniform mediump mat4 colorMatrix;
 uniform lowp float opacity;
-
 varying highp vec2 qt_TexCoord;
 
 void main()
 {
-   // For U0 Y0 V0 Y1 macropixel, lookup Y0 or Y1 based on whether
-   // the original texture x coord is even or odd.
-   mediump float Y;
-   if (fract(floor(qt_TexCoord.x * imageWidth + 0.5) / 2.0) > 0.0)
-       Y = texture2D(yuvTexture, qt_TexCoord).a;       // odd so choose Y1
-   else
-       Y = texture2D(yuvTexture, qt_TexCoord).g;       // even so choose Y0
-   mediump float Cb = texture2D(yuvTexture, qt_TexCoord).r;
-   mediump float Cr = texture2D(yuvTexture, qt_TexCoord).b;
+    mediump vec3 YUV = vec3(texture2D(yTexture, qt_TexCoord).a, texture2D(uvTexture, qt_TexCoord).rb);
 
-   mediump vec4 color = vec4(Y, Cb, Cr, 1.0);
-   gl_FragColor = colorMatrix * color * opacity;
+    gl_FragColor = colorMatrix * vec4(YUV, 1.0) * opacity;
 }
diff --git a/src/qtmultimediaquicktools/shaders/yuyvvideo.frag b/src/qtmultimediaquicktools/shaders/yuyvvideo.frag
index 72732cd66..5ce8b7366 100644
--- a/src/qtmultimediaquicktools/shaders/yuyvvideo.frag
+++ b/src/qtmultimediaquicktools/shaders/yuyvvideo.frag
@@ -1,22 +1,12 @@
-uniform sampler2D yuvTexture; // YUYV macropixel texture passed as RGBA format
-uniform mediump float imageWidth; // The YUYV texture appears to the shader with 1/2 the image width since we use the RGBA format to pass YUYV
+uniform sampler2D yTexture; // Y component passed as GL_LUMINANCE_ALPHA, in yuyv Y = r
+uniform sampler2D uvTexture; // UV component passed as RGBA macropixel, in uyvy U = g, V = a
 uniform mediump mat4 colorMatrix;
 uniform lowp float opacity;
-
 varying highp vec2 qt_TexCoord;
 
 void main()
 {
-   // For Y0 U0 Y1 V0  macropixel, lookup Y0 or Y1 based on whether
-   // the original texture x coord is even or odd.
-   mediump float Y;
-   if (fract(floor(qt_TexCoord.x * imageWidth + 0.5) / 2.0) > 0.0)
-       Y = texture2D(yuvTexture, qt_TexCoord).b;       // odd so choose Y1
-   else
-       Y = texture2D(yuvTexture, qt_TexCoord).r;       // even so choose Y0
-   mediump float Cb = texture2D(yuvTexture, qt_TexCoord).g;
-   mediump float Cr = texture2D(yuvTexture, qt_TexCoord).a;
+    mediump vec3 YUV = vec3(texture2D(yTexture, qt_TexCoord).r, texture2D(uvTexture, qt_TexCoord).ga);
 
-   mediump vec4 color = vec4(Y, Cb, Cr, 1.0);
-   gl_FragColor = colorMatrix * color * opacity;
+    gl_FragColor = colorMatrix * vec4(YUV, 1.0) * opacity;
 }