BT2020，shader该怎么修改？

shader新增对比度，饱和度，亮度调节；

Author: RealChuan

README.md

@@ -13,17 +13,30 @@
 2. 在WidgetRender中，尽可能使用QImage::Format_RGB32和QImage::Format_ARGB32_Premultiplied图像格式。如下原因：
    1. Avoid most rendering directly to most of these formats using QPainter. Rendering is best optimized to the Format_RGB32  and Format_ARGB32_Premultiplied formats, and secondarily for rendering to the Format_RGB16, Format_RGBX8888,  Format_RGBA8888_Premultiplied, Format_RGBX64 and Format_RGBA64_Premultiplied formats.
 
+### OpenGL 怎么渲染BT.2020色彩空间的图像？
+
+现在调整了对比度，饱和度，亮度；效果并不是很好。
+
+```cpp
+contrast = 1.6;
+saturation = 1.0;
+brightness = 0;
+```
+如果不调整，就跟ffplay输出图像效果一致，整体颜色偏暗。Netflix的视频，视频开头的N，显示的颜色偏暗黄色。
+
+### OpenGL 渲染图像，怎么实现画质增强的效果？
+
 ### Ffmpeg（5.0）在解码字幕与4.4.3不太一样
 
-### 解码字幕(ffmpeg-n5.0):
+#### 解码字幕(ffmpeg-n5.0):
 
 ```
 0,,en,,0000,0000,0000,,Peek-a-boo!
 ```
 
 你必须使用 ``ass_process_chunk`` 并设置 pts 和持续时间, 如在 libavfilter/vf_subtitles.c 中一样。
 
-ASS 标准格式应为(ffmpeg-n4.4.3) :
+#### ASS 标准格式应为(ffmpeg-n4.4.3) :
 
 ```
 Dialogue: 0,0:01:06.77,0:01:08.00,en,,0000,0000,0000,,Peek-a-boo!\r\n

ffmpeg/colorspace.hpp

@@ -25,7 +25,7 @@ static constexpr std::array<float, 9> kBT709Matrix
 static constexpr QVector3D kBT2020ffset = {-0.0627451017, -0.501960814, -0.501960814};
 
 static constexpr std::array<float, 9> kBT2020Matrix
-    = {1.1644, 1.1644, 1.1644, 0.000, -0.187326f, 2.141772f, 1.678674f, -0.650424f, 0.000};
+    = {1.1678, 1.1678, 1.1678, 0.0000, -0.1879, 2.1481, 1.6836, -0.6523, 0.0000};
 
 } // namespace Ffmpeg::ColorSpace
 

ffmpeg/videorender/openglrender.cc

@@ -183,6 +183,9 @@ void OpenglRender::initSubTexture()
 
 void OpenglRender::setColorSpace()
 {
+    GLfloat contrast = 1.0;
+    GLfloat saturation = 0;
+    GLfloat brightness = 0;
     auto *avFrame = d_ptr->framePtr->avFrame();
     switch (avFrame->colorspace) {
     case AVCOL_SPC_BT470BG:
@@ -196,6 +199,9 @@ void OpenglRender::setColorSpace()
         d_ptr->programPtr->setUniformValue("offset", ColorSpace::kBT2020ffset);
         d_ptr->programPtr->setUniformValue("colorConversion",
                                            QMatrix3x3(ColorSpace::kBT2020Matrix.data()));
+        contrast = 1.6;
+        saturation = 1.0;
+        brightness = 0;
         break;
     //case AVCOL_SPC_BT709:
     default:
@@ -204,6 +210,9 @@ void OpenglRender::setColorSpace()
                                            QMatrix3x3(ColorSpace::kBT709Matrix.data()));
         break;
     }
+    d_ptr->programPtr->setUniformValue("contrast", contrast);
+    d_ptr->programPtr->setUniformValue("saturation", saturation);
+    d_ptr->programPtr->setUniformValue("brightness", brightness);
 }
 
 auto OpenglRender::fitToScreen(const QSize &size) -> QMatrix4x4

ffmpeg/videorender/shader/video_nv12.frag

@@ -1,14 +1,41 @@
 #version 330 core
 
-in vec2 TexCord;         // 纹理坐标
-out vec4 FragColor;      // 输出颜色
+in vec2 TexCord;    // 纹理坐标
+out vec4 FragColor; // 输出颜色
 
 uniform sampler2D tex_y;
 uniform sampler2D tex_u;
 
 uniform vec3 offset;
 uniform mat3 colorConversion;
 
+uniform float contrast;
+uniform float saturation;
+uniform float brightness;
+
+vec3 adjustContrast(vec3 rgb, float contrast) // 对比度调整函数
+{
+    vec3 temp = rgb - vec3(0.5);
+    temp = temp * contrast;
+    temp = temp + vec3(0.5);
+    temp = clamp(temp, vec3(0.0), vec3(1.0));
+    return temp;
+}
+
+vec3 adjustSaturation(vec3 rgb, float saturation) // 饱和度调整函数
+{
+    const vec3 luminosityFactor = vec3(0.2126, 0.7152, 0.0722);
+    vec3 grayscale = vec3(dot(rgb, luminosityFactor));
+    return mix(grayscale, rgb, 1.0 + saturation);
+}
+
+vec3 adjustBrightness(vec3 rgb, float brightness) // 亮度调整函数
+{
+    vec3 temp = rgb + vec3(brightness);
+    temp = clamp(temp, vec3(0.0), vec3(1.0));
+    return temp;
+}
+
 void main()
 {
     vec3 yuv;
@@ -20,5 +47,9 @@ void main()
     yuv += offset;
     rgb = yuv * colorConversion;
 
+    rgb = adjustContrast(rgb, contrast);
+    rgb = adjustSaturation(rgb, saturation);
+    rgb = adjustBrightness(rgb, brightness);
+
     FragColor = vec4(rgb, 1.0);
 }