0028912: Visualization, TKOpenGl - multi-texture support

Graphic3d_AspectFillArea3d now stores array of textures.
Graphic3d_TextureParams stores texture unit for mapping texture.

OpenGl_Context::BindTextures() - context now manages the set of active textures.
Related code has been removed from OpenGl_Workspace.

OpenGl_Sampler has been extended to hold texture parameters structure.
OpenGl_Texture now holds OpenGl_Sampler instance as class field.
OpenGl_Texture inherits new class OpenGl_NamedResource and holds
texture identifier used for sharing resource in OpenGl_Context.

OpenGl_RaytraceGeometry now creates bindless textures taking
Sampler object directly from OpenGl_Texture.
OpenGl_Context::BindTextures() automatically recreates immutable
Sampler Object on texture parameters change.

Declared new structure OpenGl_ArbSamplerObject for platform-neutral
usage of related functionality.
Related functions are now loaded within OpenGL ES 3.0+.

Declarations.glsl - occActiveSampler has been renamed to occSampler0
with aliases occSamplerBaseColor (main) and occActiveSampler (for compatibility).
Additional texture samplers should be declared explicitly
within specific GLSL program as occSampler1, occSampler2, etc.

AIS_Shape and AIS_ColoredShape now computes Shaded presentation
with UV coordinates if texture mapping is enabled in Drawer.

vshaderprog now accepts Shader source code as parameter.

src/Shaders/Declarations.glsl

@@ -118,10 +118,13 @@ vec4  occBackMaterial_Specular(void);      //!< Specular reflection
 float occBackMaterial_Shininess(void);     //!< Specular exponent
 float occBackMaterial_Transparency(void);  //!< Transparency coefficient
 
+#define occActiveSampler    occSampler0                //!< alias for backward compatibility
+#define occSamplerBaseColor occSampler0                //!< alias to a base color texture
+uniform               sampler2D occSampler0;           //!< current active sampler;
+                                                       //!  occSampler1, occSampler2,... should be defined in GLSL program body for multitexturing
 uniform               vec4      occColor;              //!< color value (in case of disabled lighting)
 uniform THE_PREC_ENUM int       occDistinguishingMode; //!< Are front and back faces distinguished?
 uniform THE_PREC_ENUM int       occTextureEnable;      //!< Is texture enabled?
-uniform               sampler2D occActiveSampler;      //!< Current active sampler
 uniform               vec4      occTexTrsf2d[2];       //!< 2D texture transformation parameters
 uniform               float     occPointSize;          //!< point size
 

src/Shaders/Shaders_Declarations_glsl.pxx

@@ -121,10 +121,13 @@ static const char Shaders_Declarations_glsl[] =
   "float occBackMaterial_Shininess(void);     //!< Specular exponent\n"
   "float occBackMaterial_Transparency(void);  //!< Transparency coefficient\n"
   "\n"
+  "#define occActiveSampler    occSampler0                //!< alias for backward compatibility\n"
+  "#define occSamplerBaseColor occSampler0                //!< alias to a base color texture\n"
+  "uniform               sampler2D occSampler0;           //!< current active sampler;\n"
+  "                                                       //!  occSampler1, occSampler2,... should be defined in GLSL program body for multitexturing\n"
   "uniform               vec4      occColor;              //!< color value (in case of disabled lighting)\n"
   "uniform THE_PREC_ENUM int       occDistinguishingMode; //!< Are front and back faces distinguished?\n"
   "uniform THE_PREC_ENUM int       occTextureEnable;      //!< Is texture enabled?\n"
-  "uniform               sampler2D occActiveSampler;      //!< Current active sampler\n"
   "uniform               vec4      occTexTrsf2d[2];       //!< 2D texture transformation parameters\n"
   "uniform               float     occPointSize;          //!< point size\n"
   "\n"