C# Rendering OpenCL-generated image

Question

Problem: I\'m trying to render a dynamic Julia fractal in real time. Because the fractal is constantly changing, I need to be able to render at least 20 fra

Answer 1

To cover the questions: Yes, OpenCL can paint, but Monogame apparently doesn't encapsulate over the top of CL, so No to Question 1. Question 2 is the right question: maybe, see suggestions below. Question 3: HLSL is essentially PS 1.1 so "why isn't it possible" is because PS evolved to 2.x to manage parallelization through wider data pipes...so you want Dx12 support or GLSL/OpenGL.

Since you are close to your performance expectations using CLoo, why not try OpenCL.Net and/or OpenTK to bind the Julia calculations more closely to the Monogame API? --If you have to go GPU-CPU-GPU at least make that as wide a pipeline as possible.

Alternately, a slightly sideways solution to your parallelization and framerate problem might be integrating GP-GPU wrappers such as Quanta's Alea with your Monogame solution. I'd suggest looking at Cudafy, but Alea is more robust and cross-vendor GPU supported.

The build process will decide which portion of the Julia code will calculate on GPU via Alea, and the Monogame portions will receive the pixel-field for rendering. The sticking points will be library "play-nice" compatibility, and ultimately, frame-rate if you get it working.

Bottom line: you're stuck, by choice, in HLSL (read: Microsoft Dx9) and Monogame doesn't support GLSL/Dx12....so you will have to maneuver creatively to get un-stuck.

Answer 2

Sorry I do not use OpenCL nor C# but You can do this fully inside shaders using GLSL (but you might have precision problems as for Julia like fractals is sometimes even 64bit double not enough). Anyway here a simple example of Mandelbrot set I did some years back...

CPU side app C++/OpenGL/GLSL/VCL code::

//---------------------------------------------------------------------------
#include <vcl.h>
#pragma hdrstop
#include "Unit1.h" // VCL window header
#include "gl\\OpenGL3D_double.cpp" // my GL engine
//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma resource "*.dfm"
TForm1 *Form1;
OpenGLscreen scr;
GLSLprogram shd;
float mx=0.0,my=0.0,mx0=0.0,my0=0.0,mx1=0.0,my1=0.0;
TShiftState sh0,sh1;
int xs=1,ys=1;
int txrmap=-1;
float zoom=1.000;
unsigned int queryID[2];
//---------------------------------------------------------------------------
void gl_draw()
    {
    float x,y,dx,dy;
    scr.cls();
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    // matrix for old GL rendering
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    glMatrixMode(GL_TEXTURE);
    glLoadIdentity();


    // GLSL uniforms
    shd.bind();
    shd.set1i("txrmap",0);      // texture unit
    shd.set2f("p0",mx,my);      // pan position
    shd.set1f("zoom",zoom);     // zoom

    // issue the first query
    // Records the time only after all previous
    // commands have been completed
    glQueryCounter(queryID[0], GL_TIMESTAMP);

    // QUAD covering screen
    scr.txrs.bind(txrmap);
    glColor3f(1.0,1.0,1.0);
    glBegin(GL_QUADS);
    glTexCoord2f(0.0,0.0); glVertex2f(-1.0,+1.0);
    glTexCoord2f(0.0,1.0); glVertex2f(-1.0,-1.0);
    glTexCoord2f(1.0,1.0); glVertex2f(+1.0,-1.0);
    glTexCoord2f(1.0,0.0); glVertex2f(+1.0,+1.0);
    glEnd();
    shd.unbind();
    scr.txrs.unbind();

    // issue the second query
    // records the time when the sequence of OpenGL
    // commands has been fully executed
    glQueryCounter(queryID[1], GL_TIMESTAMP);


    // GL driver info and GLSL log
    scr.text_init_pix(1.0);
    glColor4f(0.0,0.2,1.0,0.8);
    scr.text(glGetAnsiString(GL_VENDOR));
    scr.text(glGetAnsiString(GL_RENDERER));
    scr.text("OpenGL ver: "+glGetAnsiString(GL_VERSION));
    glColor4f(0.4,0.7,0.8,0.8);
    for (int i=1;i<=shd.log.Length();) scr.text(str_load_lin(shd.log,i,true));
    scr.text_exit();

    scr.exe();
    scr.rfs();

    // wait until the results are available
    int e;
    unsigned __int64 t0,t1;
    for (e=0;!e;) glGetQueryObjectiv(queryID[0],GL_QUERY_RESULT_AVAILABLE,&e);
    for (e=0;!e;) glGetQueryObjectiv(queryID[1],GL_QUERY_RESULT_AVAILABLE,&e);
    glGetQueryObjectui64v(queryID[0], GL_QUERY_RESULT, &t0);
    glGetQueryObjectui64v(queryID[1], GL_QUERY_RESULT, &t1);
    Form1->Caption=AnsiString().sprintf("Time spent on the GPU: %f ms\n", (t1-t0)/1000000.0);
    }
//---------------------------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner):TForm(Owner)
    {
    scr.init(this);

    OpenGLtexture txr;
    txr.load      ("gradient.jpg");
    txrmap=scr.txrs.add(txr);

    shd.set_source_file("","","","Mandelbrot_set.glsl_vert","Mandelbrot_set.glsl_frag");

    glGenQueries(2, queryID);
    }
//---------------------------------------------------------------------------
void __fastcall TForm1::FormDestroy(TObject *Sender)
    {
    scr.exit();
    }
//---------------------------------------------------------------------------
void __fastcall TForm1::FormResize(TObject *Sender)
    {
    scr.resize();
    xs=ClientWidth;
    ys=ClientHeight;
    gl_draw();
    }
//---------------------------------------------------------------------------
void __fastcall TForm1::FormPaint(TObject *Sender)
    {
    gl_draw();
    }
//---------------------------------------------------------------------------
void __fastcall TForm1::FormMouseMove(TObject *Sender, TShiftState Shift, int X,int Y)
    {
    bool q0,q1;
    mx1=1.0-divide(X+X,xs-1);
    my1=divide(Y+Y,ys-1)-1.0;
    sh1=Shift;
    q0=sh0.Contains(ssLeft);
    q1=sh1.Contains(ssLeft);
    if (q1)
        {
        mx-=(mx1-mx0)*zoom;
        my-=(my1-my0)*zoom;
        }
    mx0=mx1; my0=my1; sh0=sh1;
    gl_draw();
    }
//---------------------------------------------------------------------------
void __fastcall TForm1::FormMouseDown(TObject *Sender, TMouseButton Button,TShiftState Shift, int X, int Y)
    {
    FormMouseMove(Sender,Shift,X,Y);
    }
//---------------------------------------------------------------------------
void __fastcall TForm1::FormMouseUp(TObject *Sender, TMouseButton Button,TShiftState Shift, int X, int Y)
    {
    FormMouseMove(Sender,Shift,X,Y);
    }
//---------------------------------------------------------------------------
void __fastcall TForm1::FormMouseWheelDown(TObject *Sender, TShiftState Shift, TPoint &MousePos, bool &Handled)
    {
    zoom*=1.2;
    gl_draw();
    }
//---------------------------------------------------------------------------
void __fastcall TForm1::FormMouseWheelUp(TObject *Sender, TShiftState Shift, TPoint &MousePos, bool &Handled)
    {
    zoom/=1.2;
    gl_draw();
    }
//---------------------------------------------------------------------------

You can ignore most of the code the important stuff is gl_draw() rendering single QUAD covering whole screen and passing zoom and pan position. This code uses old style glBegin/glEnd and default nVidia locations so it may not work on different vendor gfx drivers. The mesh should be in VAO/VBO so the layout locations will match to see how to do it take a look at the link on the end of answer or port the shaders to compatibility profile.

Vertex:

// Vertex
#version 420 core
layout(location=0) in vec2 pos;     // glVertex2f <-1,+1>
out smooth vec2 p;                  // texture end point <0,1>
void main()
    {
    p=pos;
    gl_Position=vec4(pos,0.0,1.0);
    }

Fragment:

// Fragment
#version 420 core
uniform sampler2D txrmap;           // texture unit for light map
uniform vec2 p0=vec2(0.0,0.0);      // mouse position <-1,+1>
uniform float zoom=1.000;           // zoom [-]
in smooth vec2 p;
out vec4 col;
void main()
    {
    int i,n;
    vec2 pp;
    float x,y,q,xx,yy;
    pp=(p*zoom)-p0;         // y (-1, 1)
    pp.x=(1.75*pp.x)-0.75;  // x (-2.5, 1)
    for (x=0.0,y=0.0,xx=0.0,yy=0.0,i=0,n=200;(i<n)&&(xx+yy<4.0);i++)
        {
        q=xx-yy+pp.x;
        y=(2.0*x*y)+pp.y;
        x=q;
        xx=x*x;
        yy=y*y;
        }
    q=float(i)/float(n);
    col=texture2D(txrmap,vec2(q,0.5));
//  col=vec4(q,q,q,1.0);
    }

using this texture as gradient:

Here result screenshot:

In case you need to get started with GLSL (to replace my gl engine stuff) see:

• simple complete GL+VAO/VBO+GLSL+shaders example in C++

but I am sure there must be tons of tutorials for this in C# so google

If you are interested in color enhancing see:

• Mandelbrot Set - Color Spectrum Suggestions?