I created a shader storage buffer object to give information to my vertex shader. It is bound to a buffer containing a single structure. But there is a problem. The data I keep in this structure is not a simple array, it's a std::vector.
Here is the structure :
typedef struct {
glm::mat4 modelMatrix;
} entityInfo;
typedef struct {
std::vector<entityInfo> entityInfoBuffer;
} shaderData;
mat4 is just a simple 4x4 float matrix.
If I give this to OpenGL, the data transmitted to the GPU will be just a bunch of pointers and info about the matrix/vector, and not the data in them.
One solution would be to create a structure only for OpenGL:
typedef struct {
float* modelMatrix;
} SSBOentityInfo;
typedef struct {
SSBOentityInfo* entityInfoBuffer;
} SSBOshaderData;
But I would have to copy eeeeevery pointer corresponding to the data of the containers.
Is there a better way to do it?
glm::mat4 is, for all intents and purposes, an array of 16 floats. Not a pointer to 16 floats, an actual float[16] array. 16 floats, one after the other.
Therefore, a vector<glm::mat4> manages a contiguous array of elements, where each element is 16 floats. It is that data that you want to store in your buffer object. So... do that.
vector manages a contiguous array of data, so it's perfectly legal to get a pointer to this array. That's what vector.data() is for. So that's the source pointer you give to glBufferSubData or whatever. The size would be the number of elements in the array (vector.size()) times the size of each element as computed by sizeof.