Polymorphism - Can't Articulate Problem

This is a discussion on Polymorphism - Can't Articulate Problem within the C++ Programming forums, part of the General Programming Boards category; Okay. here's a problem I can't wrap my mind around. I think I basically need all of my opengl transformations ...

  1. #1
    Registered User Tonto's Avatar
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    Polymorphism - Can't Articulate Problem

    Okay. here's a problem I can't wrap my mind around. I think I basically need all of my opengl transformations to be isolated by glPushMatrix and glPopMatrix. So I have stuff like this:

    Code:
    abstract base object has virtual void draw() = 0
    
    class stuff extends object and implements draw
    class sturf extends object and implements draw
    class stcrf extends object and implements draw
    
    application has array of objects and draws them
    I need each drawing routine to be encased in a glPushMatrix and glPopMatrix. I think I understand that this is kind of simplistic in it's approach, and even still I can't figure it out, and if there's a better design, suggestions are welcomed.

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    codez http://code.google.com/p/zxcvbn/

  2. #2
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    You could do something like this:

    Code:
    void DrawObjects(std::list<Object*> ls) {
      std::list<Object*>::iterator it;
      for(it = ls.begin(); it != ls.end(); it++) {
        glPushMatrix();
          (*it)->Draw();
        glPopMatrix();
      }
    }

  3. #3
    (?<!re)tired Mario F.'s Avatar
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    If I understood your problem, you can maintain the pure virtual but still implement it on the ABC.

    Your deriveds will then be able to implement their own draw() and call base:: Draw() from within, where appropriate.

    EDIT: Is there any way to avoid the annoyance of having to put a space to avoid the smiley on base:raw()?
    The programmer’s wife tells him: “Run to the store and pick up a loaf of bread. If they have eggs, get a dozen.”
    The programmer comes home with 12 loaves of bread.


    Originally Posted by brewbuck:
    Reimplementing a large system in another language to get a 25% performance boost is nonsense. It would be cheaper to just get a computer which is 25% faster.

  4. #4
    Cat
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    Quote Originally Posted by Tonto
    Okay. here's a problem I can't wrap my mind around. I think I basically need all of my opengl transformations to be isolated by glPushMatrix and glPopMatrix. So I have stuff like this:

    Code:
    abstract base object has virtual void draw() = 0
    
    class stuff extends object and implements draw
    class sturf extends object and implements draw
    class stcrf extends object and implements draw
    
    application has array of objects and draws them
    I need each drawing routine to be encased in a glPushMatrix and glPopMatrix. I think I understand that this is kind of simplistic in it's approach, and even still I can't figure it out, and if there's a better design, suggestions are welcomed.
    One thing you could do would be:

    Code:
    void Base::Paint(){
        BeginDraw();
        Draw();
        EndDraw();
    }
    
    virtual void Base::BeginDraw(){
        glPushMatrix();
    }
    
    virtual void Base::Draw() = 0;
    
    virtual void Base::EndDraw(){
        glPopMatrix();
    }
    If your child classes implement BeginDraw/EndDraw (to do their own init/cleanup) then they should call the base class at the beginning of BeginDraw and the end of EndDraw.
    You ever try a pink golf ball, Wally? Why, the wind shear on a pink ball alone can take the head clean off a 90 pound midget at 300 yards.

  5. #5
    The superhaterodyne twomers's Avatar
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    >> EDIT: Is there any way to avoid the annoyance of having to put a space to avoid the smiley on base:raw()?

    I can never tell when you're being sarcastic or not, so try this the next time: [noparse]:D[/noparse] I think it's not worth the effort to do. Besides, some people find that syntax aesthetic ...

    std :: vector< std :: string :: size_tpye var > d;

    Just confusing, in my opinion.

  6. #6
    (?<!re)tired Mario F.'s Avatar
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    Perfect! Thanks.

    I wasn't being sarcastic this time
    The programmer’s wife tells him: “Run to the store and pick up a loaf of bread. If they have eggs, get a dozen.”
    The programmer comes home with 12 loaves of bread.


    Originally Posted by brewbuck:
    Reimplementing a large system in another language to get a 25% performance boost is nonsense. It would be cheaper to just get a computer which is 25% faster.

  7. #7
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    Disable smilies in text. :D

  8. #8
    (?<!re)tired Mario F.'s Avatar
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    Even better, thanks!
    The programmer’s wife tells him: “Run to the store and pick up a loaf of bread. If they have eggs, get a dozen.”
    The programmer comes home with 12 loaves of bread.


    Originally Posted by brewbuck:
    Reimplementing a large system in another language to get a 25% performance boost is nonsense. It would be cheaper to just get a computer which is 25% faster.

  9. #9
    semi-colon generator ChaosEngine's Avatar
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    how about something like this

    Code:
    class DrawableObject
    {
    public:
        virtual void Draw(void) const = 0; // drawing should not affect state of object
    };
    
    // lots of classes that derive from DrawableObject and implement Draw()
    
    class GlPainter
    public:
        GlPainter(void)
        {
             glPushMatrix();
        }
    
        ~GlPainter(void)
        {
             glPopMatrix();
        }
    
        void operator()(const DrawableObject& obj)
        {
             obj->Draw();
        }
    };
    
    void DoPainting(const DrawableObject& obj)
    {
        GlPainter paint;
        paint();
    }
    
    typedef boost::ptr_vector<DrawableObject> DrawingColl;
    
    void Paint(const DrawingColl& coll)
    {
        std::for_each(coll.begin(), coll.end(), DoPainting);
    }
    while it could use some fine tuning, it has the advantage of being exception safe
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  10. #10
    Registered User Tonto's Avatar
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    For some reason I didn't really understand that I could just do exactly what Desolation mentioned. Haha. But, there are lots of ways to do it, as you guys have shown. That begindraw/enddraw thing could be useful if specialized initialization would be necessary, and the safety of ce's is good. I may consider looking into boost libraries some time.

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    ╚╝╚╩╝╚╩╝╚╩╝╚╩╝

    codez http://code.google.com/p/zxcvbn/

  11. #11
    (?<!re)tired Mario F.'s Avatar
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    On top of that, check also the Bridge Pattern. I'm not quiet sure if it isn't too much for your current needs, but sure makes an interesting reading for more complex needs.
    The programmer’s wife tells him: “Run to the store and pick up a loaf of bread. If they have eggs, get a dozen.”
    The programmer comes home with 12 loaves of bread.


    Originally Posted by brewbuck:
    Reimplementing a large system in another language to get a 25% performance boost is nonsense. It would be cheaper to just get a computer which is 25% faster.

  12. #12
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    Using this simple class (or some variant of it), is a simple addition to Desolation's code that makes at least the popping of the matrix exception safe:
    Code:
    class GlPainter {
    public:
        GlPainter(void)
        {
             glPushMatrix();
        }
        ~GlPainter(void)
        {
             glPopMatrix();
        }
    };
    
    void DrawObjects(std::list<Object*> ls) {
      std::list<Object*>::iterator it;
      for(it = ls.begin(); it != ls.end(); it++) {
        GlPainter paint;
        (*it)->Draw();
      }
    }

  13. #13
    Cat without Hat CornedBee's Avatar
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    I don't get the point of the bridge pattern.

    Anyway, here's another thing you can do:
    Code:
    class Drawable
    {
    public:
      void draw() {
        glPushMatrix();
        do_draw();
        glPopMatrix();
      }
    protected:
      virtual void do_draw() = 0;
    };
    Subclasses override not draw() but do_draw(). Because do_draw() is protected, it cannot be called directly from the outside; all calls must go through draw(), which performs the wrapping operation.
    All the buzzt!
    CornedBee

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  14. #14
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    I like that option the best. You might actually want to make do_draw private instead of protected. There shouldn't be any do_draw-ing happening outside of the draw() function.

  15. #15
    (?<!re)tired Mario F.'s Avatar
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    > I don't get the point of the bridge pattern.

    Could you elaborate on that CornedBee?
    The programmer’s wife tells him: “Run to the store and pick up a loaf of bread. If they have eggs, get a dozen.”
    The programmer comes home with 12 loaves of bread.


    Originally Posted by brewbuck:
    Reimplementing a large system in another language to get a 25% performance boost is nonsense. It would be cheaper to just get a computer which is 25% faster.

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