Question

I could not figure out how to dereference this pointer…

sizeof(shapetest2->tripsName) in this line below, it is obviously not going to work because it is a pointer, i could not figure out how to dereference it? (is it easy? or is it a couple steps?, i’ve tried several things, but could not get close) I am not an experience enough coder to figure this particular circumstance out.

glBufferSubData(GL_ELEMENT_ARRAY_BUFFER, 0, sizeof(shapetest2->tripsName), shapetest2->tripsName);

here is the setup code. (i am experimenting with a VOB in openGL ES 1.5, so if it looks odd, that is why) if i forgot some important setup or definitions, or code, let me know and i’ll include it.

GLsizeiptr dataSize;
GLsizeiptr indexSize;

typedef struct shapeBase {
    void *stripsName[maxStrips];
    void *tripsName;
    void *fansName;
    int   totStrips;
    int   stripsNum[maxStrips];
    int   tripsNum;
    int   totFans;
    int   fansBgn[maxStrips];
    int   fansNum[maxStrips];
    void *dataName;
    void *listOfInserts;
    Vertex3D center;
    Vertex3D radius;
    int   damageMax;
    float weight;
    GLuint bufferName;
    GLuint indexName;
} shapeBase;

static const GLushort test2Trips[] =
{
    0, 1, 3, 1, 2, 3,
    4, 5, 7, 5, 6, 7,
    8, 9, 11, 9, 10, 11,
    12, 13, 15, 13, 14, 15,
    16, 17, 19, 17, 18, 19,
    20, 21, 23, 21, 22, 23,
    24, 25, 27, 25, 26, 27,
    28, 29, 31, 29, 30, 31,
    32, 33, 35, 33, 34, 35,
    36, 37, 39, 37, 38, 39,
    40, 41, 43, 41, 42, 43,
    44, 45, 47, 45, 46, 47,
};

//-------------------------
static inline void shapetest2Setup(void)
{
    shapetest2 = malloc(sizeof(shapeBase));
    shapetest2->stripsName[1]   = NULL;
    shapetest2->tripsName       = &test2Trips;
    shapetest2->fansName        = NULL;
    shapetest2->dataName        = &test2Data;
    shapetest2->totStrips       = 0;
    shapetest2->stripsNum[1]    = 0;
    shapetest2->tripsNum        = 72;
    shapetest2->totFans     = 0;
    shapetest2->listOfInserts   = NULL;
    shapetest2->center      = Vertex3DMake( 0.000000, -0.000000, 2.000000 );
    shapetest2->radius      = Vertex3DMake( 1.000000, 1.000000, 2.000000 );

    dataSize = sizeof(test1Data) + sizeof(test2Data);

    glGenBuffers(1, &mainBuffer);
    glBindBuffer(GL_ARRAY_BUFFER, mainBuffer);
    glBufferData(GL_ARRAY_BUFFER, dataSize, NULL, GL_STATIC_DRAW);

    glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(test1Data), test1Data);
    glBufferSubData(GL_ARRAY_BUFFER, sizeof(test1Data), sizeof(test2Data), test2Data);

//  glGenBuffers(1, &shapetest2->indexName);
//  glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, shapetest2->indexName);
//  glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(test2Trips), test2Trips, GL_STATIC_DRAW);


    indexSize = sizeof(test1Trips) + sizeof(test2Trips);

    glGenBuffers(1, &mainIndex);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, mainIndex);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, indexSize, NULL, GL_STATIC_DRAW);
}


//------------------------------------------------------
static inline void DrawOutShape(void)
{
    glBindBuffer(GL_ARRAY_BUFFER, mainBuffer);


    glVertexPointer(3, GL_FLOAT, sizeof(VertexData3D), (void*)0);
    glNormalPointer(GL_FLOAT, sizeof(VertexData3D), (void*)12);

    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, mainIndex);

//  glBufferSubData(GL_ELEMENT_ARRAY_BUFFER, 0, sizeof(theInsert->insertName->tripsName), theInsert->insertName->tripsName);

//  glBufferSubData(GL_ELEMENT_ARRAY_BUFFER, 0, sizeof(test1Trips), test1Trips);
//  glBufferSubData(GL_ELEMENT_ARRAY_BUFFER, sizeof(test1Trips), sizeof(test2Trips), shapetest2->tripsName);

    glBufferSubData(GL_ELEMENT_ARRAY_BUFFER, 0, sizeof(shapetest2->tripsName), shapetest2->tripsName);


         glDrawElements(GL_TRIANGLES, theInsert->insertName->tripsNum, GL_UNSIGNED_SHORT, (void*)0);


    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);


polys += theInsert->insertName->tripsNum;

}

(theInsert is a handle (pointer to pointer) of the shapetest2, so you can substitute shapetest2 if you see “theInsert->insertName”)

if i comment out the offending line, and uncomment the line above, it is working, but i need this indirection, (and actually i need another level of indirection that you can see in another commented out line) but if i can figure out how to dereference this line, i should be able to do it for another level of indirection?)

Answer 1

sizeof is compile-time constant that works on exact type you provide. sizeof of void* is just a size of pointer on your machine (likely 4/8 bytes). Just store size along with other data.