OpenGLVideo: Move colourspace primary conversion into subroutine

- in preparation for extending functionality

mythtv/libs/libmythtv/openglvideo.cpp

@@ -310,12 +310,6 @@ bool OpenGLVideo::CreateVideoShader(VideoShaderType Type, MythDeintType Deint)
             defines << "YUY2";
         }
 
-        // if primaries are disabled, the primaries conversion matrix will be identity
-        // and we can optimise out the conversion.
-        QMatrix4x4 primaries = m_videoColourSpace->GetPrimaryMatrix();
-        if (!primaries.isIdentity())
-            defines << "PRIMARIES";
-
 #ifdef USING_VTB
         // N.B. Rectangular texture support is only currently used for VideoToolBox
         // video frames which are NV12. Do not use rectangular textures for the 'default'
@@ -380,6 +374,9 @@ bool OpenGLVideo::CreateVideoShader(VideoShaderType Type, MythDeintType Deint)
             }
         }
 
+        // Retrieve colour mappping defines
+        defines << m_videoColourSpace->GetColourMappingDefines();
+
         // Add defines
         QString glsldefines;
         foreach (QString define, defines)
@@ -399,8 +396,9 @@ bool OpenGLVideo::CreateVideoShader(VideoShaderType Type, MythDeintType Deint)
         QString glslsamplers;
         for (int i = start; i < end; ++i)
             glslsamplers += QString("uniform sampler2D s_texture%1;\n").arg(i);
-        fragment = glsldefines + YUVFragmentExtensions + glslsamplers + fragment;
 
+        // construct the final shader string
+        fragment = glsldefines + YUVFragmentExtensions + glslsamplers + fragment;
     }
 
     m_shaderCost[Type] = cost;

mythtv/libs/libmythtv/openglvideoshaders.h

@@ -53,10 +53,17 @@ static const QString YUVFragmentShader =
 "uniform highp mat4 m_colourMatrix;\n"
 "uniform highp vec4 m_frameData;\n"
 "varying highp vec2 v_texcoord0;\n"
-"#ifdef MYTHTV_PRIMARIES\n"
+"#ifdef MYTHTV_COLOURMAPPING\n"
 "uniform highp mat4 m_primaryMatrix;\n"
 "uniform highp float m_colourGamma;\n"
 "uniform highp float m_displayGamma;\n"
+"highp vec4 ColourMap(highp vec4 color)\n"
+"{\n"
+"    highp vec4 res = clamp(color, 0.0, 1.0);\n"
+"    res.rgb = pow(res.rgb, vec3(m_colourGamma));\n"
+"    res = m_primaryMatrix * res;\n"
+"    return vec4(pow(res.rgb, vec3(m_displayGamma)), res.a);\n"
+"}\n"
 "#endif\n"
 
 // Chroma for lines 1 and 3 comes from line 1-2
@@ -174,10 +181,8 @@ static const QString YUVFragmentShader =
 "    gl_FragColor = vec4(mix(yuv.arb, yuv.grb, step(fract(v_texcoord0.x * m_frameData.y), 0.5)), 1.0) * m_colourMatrix;\n"
 "#else\n"
 "    gl_FragColor = yuv * m_colourMatrix;\n"
-"#ifdef MYTHTV_PRIMARIES\n"
-"    gl_FragColor.rgb = pow(max(vec3(0), gl_FragColor.rgb), vec3(m_colourGamma));\n"
-"    gl_FragColor     = max(vec4(0), m_primaryMatrix * gl_FragColor);\n"
-"    gl_FragColor.rgb = pow(gl_FragColor.rgb, vec3(m_displayGamma));\n"
+"#ifdef MYTHTV_COLOURMAPPING\n"
+"    gl_FragColor = ColourMap(gl_FragColor);\n"
 "#endif\n"
 "#endif\n"
 "}\n";

mythtv/libs/libmythtv/videocolourspace.cpp

@@ -429,6 +429,16 @@ void VideoColourSpace::SetAlpha(int Value)
     Update();
 }
 
+QStringList VideoColourSpace::GetColourMappingDefines(void)
+{
+    QStringList result;
+    if (m_primaryMatrix.isIdentity())
+        return result;
+
+    result << "COLOURMAPPING";
+    return result;
+}
+
 QMatrix4x4 VideoColourSpace::GetPrimaryMatrix(void)
 {
     return m_primaryMatrix;
@@ -549,6 +559,8 @@ inline float CalcRy(const float By, const float Gy)
  *
  * This is a joyous mindbender. There are various explanations on the interweb
  * but this is based on the Kodi implementation - with due credit to Team Kodi.
+ *
+ * \note We use QMatrix4x4 because QMatrix3x3 has no inverted method.
  */
 QMatrix4x4 VideoColourSpace::RGBtoXYZ(ColourPrimaries Primaries)
 {

mythtv/libs/libmythtv/videocolourspace.h

@@ -20,14 +20,15 @@ class VideoColourSpace : public QObject, public QMatrix4x4, public ReferenceCoun
   public:
     explicit VideoColourSpace(VideoColourSpace *Parent = nullptr);
 
-    bool  UpdateColourSpace(const VideoFrame *Frame);
+    bool          UpdateColourSpace(const VideoFrame *Frame);
     PictureAttributeSupported SupportedAttributes(void) const;
-    void  SetSupportedAttributes(PictureAttributeSupported Supported);
-    int   GetPictureAttribute(PictureAttribute Attribute);
-    void  SetAlpha(int Value);
-    QMatrix4x4 GetPrimaryMatrix(void);
-    float GetColourGamma(void);
-    float GetDisplayGamma(void);
+    void          SetSupportedAttributes(PictureAttributeSupported Supported);
+    int           GetPictureAttribute(PictureAttribute Attribute);
+    void          SetAlpha(int Value);
+    QMatrix4x4    GetPrimaryMatrix(void);
+    QStringList   GetColourMappingDefines(void);
+    float         GetColourGamma(void);
+    float         GetDisplayGamma(void);
     PrimariesMode GetPrimariesMode(void);
 
     struct ColourPrimaries