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Thread: Particle simulation [OpenGl, Cuda, Shaders]

  1. #1
    Junior Member Newbie
    Join Date
    Dec 2011
    Posts
    2

    Particle simulation [OpenGl, Cuda, Shaders]

    Hi,
    I try to create particle simulation (I'm beginner with OpenGl and Cuda). In my simulation I use code from Cuda Sdk (Particles).
    OK, let me explain my problem: I render 1k particles and move them. Everything works fine until particle are near the center of coordinate system...
    The problem is that they grow(each particle has const radius so its unexpected situation - picture below)... and I really don't know why.

    Can u help me?


    Bigger size

    My code:

    function void init()
    Code :
    GLuint pointsVBO;
    float3 *pointsVBO_device; // device pointer for VBO
    struct cudaGraphicsResource *pointsVBO_Resource;
    const float radius = 0.2;
     
    void init(void)
    {
        GLenum err = glewInit();
        if (GLEW_OK != err) exit(0);
     
        initializePositionsAndVelocities();
     
        void **v_device_addr;
        cudaGetSymbolAddress ((void **)&v_device_addr, "v_device");
        cudaMemcpy (v_device_addr, velocities, sizeof(float3) * N,  cudaMemcpyHostToDevice );
     
        glGenBuffers(1,&pointsVBO);
        glBindBuffer(GL_ARRAY_BUFFER, pointsVBO);
        glBufferData(GL_ARRAY_BUFFER, sizeof(points), points, GL_STREAM_DRAW);	
     
        cudaGraphicsGLRegisterBuffer(&pointsVBO_Resource, pointsVBO, cudaGraphicsMapFlagsNone );
     
        glEnable(GL_BLEND);
        glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);		
        glShadeModel(GL_SMOOTH);
        glClearColor(0.0f,0.0f,0.0f,0.0f);
        glClearDepth(1.0f);
        glDisable(GL_DEPTH_TEST);
        glHint(GL_PERSPECTIVE_CORRECTION_HINT,GL_NICEST);
        glHint(GL_POINT_SMOOTH_HINT,GL_NICEST);
    }

    function compileProgram()
    Code :
    GLuint compileProgram(const char *vsource, const char *fsource)
    {
        GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER);
        GLuint fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
     
        glShaderSource(vertexShader, 1, &vsource, 0);
        glShaderSource(fragmentShader, 1, &fsource, 0);
     
        glCompileShader(vertexShader);
        glCompileShader(fragmentShader);
     
        GLuint program = glCreateProgram();
     
        glAttachShader(program, vertexShader);
        glAttachShader(program, fragmentShader);
     
        glLinkProgram(program);
     
        // check if program linked
        GLint success = 0;
        glGetProgramiv(program, GL_LINK_STATUS, &success);
     
        if (!success) {
            char temp[256];
            glGetProgramInfoLog(program, 256, 0, temp);
            printf("Failed to link program:\n%s\n", temp);
            glDeleteProgram(program);
            program = 0;
        }
     
        return program;
    }

    function renderScene()
    Code :
    void renderScene(void)
    {
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
     
        glEnable(GL_POINT_SPRITE_ARB);
        glTexEnvi(GL_POINT_SPRITE_ARB, GL_COORD_REPLACE_ARB, GL_TRUE);
        glEnable(GL_VERTEX_PROGRAM_POINT_SIZE_NV);
        glDepthMask(GL_TRUE);
        glEnable(GL_DEPTH_TEST);
     
        GLuint program = compileProgram(vertexShader, spherePixelShader);
        float fov = 60;
     
        glUseProgram(program);
        glUniform1f(glGetUniformLocation(program, "pointScale"), 
                parameter.height / tanf(fov*0.5f*(float)M_PI/180.0f));
        glUniform1f(glGetUniformLocation(program, "pointRadius"), radius);
     
        glColor3f(1, 1, 0);
        glBindBufferARB(GL_ARRAY_BUFFER_ARB, pointsVBO);
        glEnableClientState(GL_VERTEX_ARRAY);                
        glVertexPointer(3, GL_FLOAT, 0, 0);
        glDrawArrays(GL_POINTS, 0, N);
        glBindBufferARB(GL_ARRAY_BUFFER_ARB, 0);
        glDisableClientState(GL_VERTEX_ARRAY); 
     
        glUseProgram(0);
        glDisable(GL_POINT_SPRITE_ARB);
        glutSwapBuffers();
    }

    shader
    Code :
    #define STRINGIFY(A) #A
     
    // vertex shader
    const char *vertexShader = STRINGIFY(
    uniform float pointRadius;  // point size in world space
    uniform float pointScale;   // scale to calculate size in pixels
    uniform float densityScale;
    uniform float densityOffset;
    void main()
    {
        // calculate window-space point size
        vec3 posEye = vec3(gl_ModelViewMatrix * vec4(gl_Vertex.xyz, 1.0));
        float dist = length(posEye);
        gl_PointSize = pointRadius * (pointScale / dist);
     
        gl_TexCoord[0] = gl_MultiTexCoord0;
        gl_Position = gl_ModelViewProjectionMatrix * vec4(gl_Vertex.xyz, 1.0);
     
        gl_FrontColor = gl_Color;
    }
    );
     
    // pixel shader for rendering points as shaded spheres
    const char *spherePixelShader = STRINGIFY(
    void main()
    {
        const vec3 lightDir = vec3(0.577, 0.577, 0.577);
     
        // calculate normal from texture coordinates
        vec3 N;
        N.xy = gl_TexCoord[0].xy*vec2(2.0, -2.0) + vec2(-1.0, 1.0);
        float mag = dot(N.xy, N.xy);
        if (mag > 1.0) discard;   // kill pixels outside circle
        N.z = sqrt(1.0-mag);
     
        // calculate lighting
        float diffuse = max(0.0, dot(lightDir, N));
     
        gl_FragColor = gl_Color * diffuse;
    }
    );

  2. #2
    Advanced Member Frequent Contributor
    Join Date
    Apr 2010
    Posts
    751

    Re: Particle simulation [OpenGl, Cuda, Shaders]

    Your shader sets gl_PointSize based on their position, so they don't have exactly constant radius

    I guess dist goes to zero and hence gl_PointSize is set to a large value.

  3. #3
    Junior Member Newbie
    Join Date
    Dec 2011
    Posts
    2

    Re: Particle simulation [OpenGl, Cuda, Shaders]

    Omg, of course, now I see it.
    Thanks very much.

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