Why is my object not displayed if the vertices are created manually (malloc'd then initialized), but will render if statically assigned?

Question

Ultimately, I try to use a single image for texturing several objects (hexagons) by supplying different texture coordinates to each object.
Using OpenGL ES 2.0 and GLKit, I came up with a way to do this, only to find that for some reason the objects will not be displayed if I malloc and initialize Vertex arrays manually. I especially don’t understand why this is happening because the statically assigned version of the vertex arrays is working fine.

Above is the structure I am using:

typedef struct { GLKVector3 position; GLKVector4 color; GLKVector2 texCoords; }Vertex; 

So, if I do this in a hexagon implementation, I can see various hexagons with the texture applied:

 Vertex _Vertices[] = { {{ 0, 0, 0}, {1, 1, 1, 0}, {0.50, 0.50}},//Z {{ 1, 0, 0}, {1, 1, 1, 0}, {1.00, 0.50}},//A {{ 0.5, -0.866, 0}, {1, 1, 1, 0}, {0.75, 0.00}},//B {{-0.5, -0.866, 0}, {1, 1, 1, 0}, {0.25, 0.00}},//C {{-1, 0, 0}, {1, 1, 1, 0}, {0, 0.50}},//D {{-0.5, 0.866, 0}, {1, 1, 1, 0}, {0.25, 1.00}},//E {{ 0.5, 0.866, 0}, {1, 1, 1, 0}, {0.75, 1.00}} //F }; 

However, if I comment on the above declaration instead and add an instance variable with the same name (Vertices * Vertex instead of Vertex Vertex [], since I cannot malloc for the array directly), then do the following: does nothing:

 -(void)setVertices{ _Vertices = malloc(sizeof(Vertex) * 7); //Z _Vertices[0].position.x = 0; _Vertices[0].position.y = 0; _Vertices[0].position.z = 0; _Vertices[0].color.r = 1; _Vertices[0].color.g = 1; _Vertices[0].color.b = 1; _Vertices[0].color.a = 0; _Vertices[0].texCoords.x = 0.5; _Vertices[0].texCoords.y = 0.5; //A _Vertices[1].position.x = 1; _Vertices[1].position.y = 0; _Vertices[1].position.z = 0; _Vertices[1].color.r = 1; _Vertices[1].color.g = 1; _Vertices[1].color.b = 1; _Vertices[1].color.a = 0; _Vertices[1].texCoords.x = 1; _Vertices[1].texCoords.y = 0.5; //B _Vertices[2].position.x = 0.5; _Vertices[2].position.y = -0.866; _Vertices[2].position.z = 0; _Vertices[2].color.r = 1; _Vertices[2].color.g = 1; _Vertices[2].color.b = 1; _Vertices[2].color.a = 0; _Vertices[2].texCoords.x = 0.75; _Vertices[2].texCoords.y = 0.00; //C _Vertices[3].position.x = -0.5; _Vertices[3].position.y = -0.866; _Vertices[3].position.z = 0; _Vertices[3].color.r = 1; _Vertices[3].color.g = 1; _Vertices[3].color.b = 1; _Vertices[3].color.a = 0; _Vertices[3].texCoords.x = 0.25; _Vertices[3].texCoords.y = 0; //D _Vertices[4].position.x = -1; _Vertices[4].position.y = 0; _Vertices[4].position.z = 0; _Vertices[4].color.r = 1; _Vertices[4].color.g = 1; _Vertices[4].color.b = 1; _Vertices[4].color.a = 0; _Vertices[4].texCoords.x = 0; _Vertices[4].texCoords.y = 0.5; //E _Vertices[5].position.x = -0.5; _Vertices[5].position.y = 0.866; _Vertices[5].position.z = 0; _Vertices[5].color.r = 1; _Vertices[5].color.g = 1; _Vertices[5].color.b = 1; _Vertices[5].color.a = 0; _Vertices[5].texCoords.x = 0.25; _Vertices[5].texCoords.y = 1; //F _Vertices[6].position.x = 0.5; _Vertices[6].position.y = 0.866; _Vertices[6].position.z = 0; _Vertices[6].color.r = 1; _Vertices[6].color.g = 1; _Vertices[6].color.b = 1; _Vertices[6].color.a = 0; _Vertices[6].texCoords.x = 0.75; _Vertices[6].texCoords.y = 1; } 

Here is my setup function:

 -(void)setupGL{ self.effect = [[GLKBaseEffect alloc] init]; glGenBuffers(1, &_vertexBuffer); glBindBuffer(GL_ARRAY_BUFFER, _vertexBuffer); glBufferData(GL_ARRAY_BUFFER, sizeof(_Vertices), _Vertices, GL_STATIC_DRAW); glGenBuffers(1, &_indexBuffer); glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, _indexBuffer); glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(_Indices), _Indices, GL_STATIC_DRAW); } 

And here is my drawing function:

 -(void)draw{ glPushGroupMarkerEXT(0,"drawHex"); _effect.texture2d0.envMode = GLKTextureEnvModeReplace; _effect.texture2d0.target = GLKTextureTarget2D; _effect.texture2d0.name = _texture.name; [self.effect prepareToDraw]; glBindBuffer(GL_ARRAY_BUFFER, _vertexBuffer); glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, _indexBuffer); glEnableVertexAttribArray(GLKVertexAttribPosition); glVertexAttribPointer(GLKVertexAttribPosition, 3, GL_FLOAT, GL_FALSE, sizeof(Vertex), (const GLvoid *) offsetof(Vertex, position)); glEnableVertexAttribArray(GLKVertexAttribColor); glVertexAttribPointer(GLKVertexAttribColor, 4, GL_FLOAT, GL_FALSE, sizeof(Vertex), (const GLvoid *) offsetof(Vertex, color)); glEnableVertexAttribArray(GLKVertexAttribTexCoord0); glVertexAttribPointer(GLKVertexAttribTexCoord0, 2, GL_FLOAT, GL_FALSE, sizeof(Vertex), (const GLvoid *) offsetof(Vertex, texCoords)); //draw glDrawElements(GL_TRIANGLES, sizeof(_Indices)/sizeof(_Indices[0]),GL_UNSIGNED_BYTE, 0); glPopGroupMarkerEXT(); } 

If this is important, a texture is created outside the object, and then a pointer is passed to it. Creating such a texture:

 -(void)setTextureImage:(UIImage *)image { NSError *error; _hexTexture = [GLKTextureLoader textureWithCGImage:image.CGImage options:nil error:&error]; if (error) { NSLog(@"Error loading texture from image: %@",error); }} 

I am new to all of this and it becomes very frustrating, trying to understand what is happening here.

In my huge search that I saw something about "capturing opengl es frame", but it doesn't seem to be turned on for the iphone simulator in Xcode, so I can't get it: (

I would really like to know why this is happening.

I can provide more code or explanations if this helps.

Any thoughts?

Answer 1

About the glBufferData parameter, sizeof (_Vertices) does not match between static and dynamic. If you want to use dynamic, you should use sizeof (Vertex) * 7 instead of sizeof (_Vertices).