Is there a quicker way to convert the following data into a c style pointer array?
GLfloat verticalLines [] = {
0.59, 0.66, 0.0,
0.59, -0.14, 0.0
}
My current approach is to manually iterate over the data using the method below:
-(GLfloat *)updateLineVertices{
int totalVertices = 6;
GLfloat *lineVertices = (GLfloat *)malloc(sizeof(GLfloat) * (totalVertices));
for (int i = 0; i<totalVertices; i++) {
lineVertices[i] = verticalLines[i];
}
return lineVertices;
}
Some additional info.
Ultimately I will need the data in a format which can be easily manipulated, for example:
-(void)scaleLineAnimation{
GLfloat *lineVertices = [self updateLineVertices];
for (int i = 0; i<totalVertices; i+=3) {
lineVertices[i+1] += 0.5; //scale y axis
}
}
It depends on if verticalLines is going to stick around or not. If it's defined like it is above and it's not going to change, you can forgo the whole malloc and just point lineVertices to it.
linesVertices = &verticalLines[0]
if verticalLines is going to change, you probably want your own copy, so you've got no choice but to copy the actual data from one part of memory to another as you are doing, that being said, this might be a bit more elegant
for (int i = 0; i<totalVertices; i++){
lineVertices[i] = verticalLines[i];
}
or the preferred method is probably to use memcopy(), here is some working code
//MemcopyTest.c
#include <cstdlib>
#include <stdio.h>
#include <string.h>
int main(){
float a[] = {1.0,2.0,3.0}; //Original Array
int size = sizeof(float)*3;
float *b = (float*)malloc(size); //Allocate New Array
memcpy(b, a, size); //Copy Data
for(int i = 0; i<3; i++){
printf("%f\n", b[i]);
}
free(b);
}
What's wrong with just using verticalLines directly? Anything of type T ident[n] can be implicitly converted to T* ident as if you had written &ident[0]. And if you really want to be explicit, you can just write &ident[0] directly.
Related
I usually program in java or c++ and I recently started with objective-c. Looking for vectors in objective-c, I found NSMutableArray which seems to be the best option. I'm working on an opengl game and I'm trying to create an NSMutableArray of textured quads for my sprites. Here is the relevant code:
I define textured quads:
typedef struct {
CGPoint geometryVertex;
CGPoint textureVertex;
} TexturedVertex;
typedef struct {
TexturedVertex bl;
TexturedVertex br;
TexturedVertex tl;
TexturedVertex tr;
} TexturedQuad;
I create an array in the interface:
#interface Sprite() {
NSMutableArray *quads;
}
I initiate the array and I create the texturedQuads based on "width" and "height", which are the dimensions of a single sprite, and "self.textureInfo.width" and "self.textureInfo.height", which are the dimensions of the entire sprite sheet:
quads = [NSMutableArray arrayWithCapacity:1];
for(int x = 0; x < self.textureInfo.width/width; x++) {
for(int y = 0; y < self.textureInfo.height/height; y++) {
TexturedQuad q;
q.bl.geometryVertex = CGPointMake(0, 0);
q.br.geometryVertex = CGPointMake(width, 0);
q.tl.geometryVertex = CGPointMake(0, height);
q.tr.geometryVertex = CGPointMake(width, height);
int x0 = (x*width)/self.textureInfo.width;
int x1 = (x*width + width)/self.textureInfo.width;
int y0 = (y*height)/self.textureInfo.height;
int y1 = (y*height + height)/self.textureInfo.height;
q.bl.textureVertex = CGPointMake(x0, y0);
q.br.textureVertex = CGPointMake(x1, y0);
q.tl.textureVertex = CGPointMake(x0, y1);
q.tr.textureVertex = CGPointMake(x1, y1);
//add q to quads
}
}
The problem is I don't know how to add the quad "q" to the array "quads". Simple writing [quads addObject:q] doesn't work because the parameter should be an id not a TexturedQuad. I've seen examples of how to make an id from an int etc, but I don't know how to do it with an object like my TexturedQuad.
The essence of it is that you wrap your C struct in an Obj-C class. The Obj-C class to use is NSValue.
// assume ImaginaryNumber defined:
typedef struct {
float real;
float imaginary;
} ImaginaryNumber;
ImaginaryNumber miNumber;
miNumber.real = 1.1;
miNumber.imaginary = 1.41;
// encode using the type name
NSValue *miValue = [NSValue value: &miNumber withObjCType:#encode(ImaginaryNumber)];
ImaginaryNumber miNumber2;
[miValue getValue:&miNumber2];
See here for more information.
As #Bersaelor pointed out, if you need better performance use pure C or switch to Obj-C++ and use vectors instead of Obj-C objects.
An NSMutableArray takes any NSObject* but not just structs.
If you're serious about programming in Objective-C, take a look at some tutorials.
Furthermore, NSMutableArrays are meant for convenience, if your adding/deleting a lot of objects to that Array, use plain C-stacks.
Especially for your use-case that more low-level approach will get better performance.
Keep in mind, Objective-C(++) is just a superset of C(++), so you can use any C(++) code you are already familiar with.
When I wrote my game tactica for iOS, I switched to C-Code whenever I had to do heavy lifting (i.e. recursive AI-functions that get called hundreds of times per second).
Is there a way to declare a 2D array of integers in two steps? I am having an issue with scope. This is what I am trying to do:
//I know Java, so this is an example of what I am trying to replicate:
int Array[][];
Array = new int[10][10];
Now, in OBJ-C I want to do something similar, but I cant get the syntax right. Right now I have it in one step, but I cannot use it outside of the If-Statement in which I currently have it:
int Array[10][10]; //This is based on an example I found online, but I need
//to define the size on a seperate line than the allocation
Can anyone help me out with this? I know its probably a more basic question, but you can't use the keyword "new" outside of a message (to my knowledge) and you cant send messages to ints. :(
*EDIT 1:**
My problem is scope related.
//Declare Array Somehow
Array[][] //i know this isn't valid, but I need it without size
//if statement
if(condition)
Array[1][2]
else
Array[3][4]
//I need to access it outside of those IFs
//... later in code
Array[0][0] = 5;
This is my preferred way of creating a 2D array, if you know the size of one of the boundaries:
int (*myArray)[dim2];
myArray = calloc(dim1, sizeof(*myArray));
And it can be freed in one call:
free(myArray);
Unfortunately, one of the bounds MUST be fixed for this to work.
However, if you don't know either of the boundaries, this should work too:
static inline int **create2dArray(int w, int h)
{
size_t size = sizeof(int) * 2 + w * sizeof(int *);
int **arr = malloc(size);
int *sizes = (int *) arr;
sizes[0] = w;
sizes[1] = h;
arr = (int **) (sizes + 2);
for (int i = 0; i < w; i++)
{
arr[i] = calloc(h, sizeof(**arr));
}
return arr;
}
static inline void free2dArray(int **arr)
{
int *sizes = (int *) arr;
int w = sizes[-2];
int h = sizes[-1];
for (int i = 0; i < w; i++)
free(arr[i]);
free(&sizes[-2]);
}
The declaration you showed (e.g. int Array[10][10];) is OK, and will be valid for the scope it was declared to, if you do it in a class scope, then it will be valid for the whole class.
If the size of the array varies, either use dynamic allocation (e.g. malloc and friends) or use NSMutableArray (for non-primitive data types)
I've got a c-array of CGPoints in a struct. I need to replace this array when another CGPoint is added. I'd swear I'm doing this right and it seems to work fine a few times but eventually I'll get a EXC_BAD_ACCESS. What am I missing?
Here's the struct, which I've truncated to remove a lot of items that don't pertain.
typedef struct{
CGPoint **focalPoints;
NSUInteger focalPointCount;
CGRect boundingRect;
}FocalPoints;
Here's how I initialize it:
CGPoint *fPoints = (CGPoint *)malloc(sizeof(CGPoint));
FocalPoints focalInfo = {&fPoints, 0, rect};
Note that focalInfo is passed by reference to another function, like so: anotherFunction(&focalInfo).
Now here's the function that replaces the Points array with a new one:
void AddFocalPoint (CGPoint focalPoint, FocalPoints *focal){
if (focalPoint.x == CGFLOAT_MAX) return;
if (!CGRectContainsPoint(focal->boundingRect, focalPoint)) return;
int origCount = focal->focalPointCount;
int newCount = origCount + 1;
CGPoint *newPoints = (CGPoint *) malloc((newCount) * sizeof(CGPoint));
for (int i = 0; i < newCount; i++)
newPoints[i] = (i < origCount) ? *focal->focalPoints[i] : focalPoint; //error occurs here
free(*focal->focalPoints);
*focal->focalPoints = newPoints;
focal->focalPointCount = newCount;
}
The EXC_BAD_ACCESS error occurs in the above code on line 8: newPoints[i] = (i < origCount) ? *focal->focalPoints[i] : focalPoint;. So what exactly am I doing wrong?
This is a bit of a long shot, but maybe there's an issue with operator priority in *focal->focalPoints[i]. Have you try adding parentheses according to what you are trying to achieve ?
I believe the issue comes with where GCPoint *fPoints allocated as &fPoints evaluates to an address of that ... which is no longer valid once the function exits.
(The data to which it points was allocated fine with malloc.)
Aside from the suggestion I made in a comment, of using a linked list/NSMutableArray, my other suggestion would be that you use realloc() instead of constantly using malloc(), copying by hand, and then free()ing the old allocation.
void * realloc(void *ptr, size_t size);
The realloc() function tries to change the size of the allocation pointed to by ptr to size, and returns ptr. If there is not enough room to enlarge the memory allocation pointed to by ptr, realloc() creates a new allocation, copies as much of the old data pointed to by ptr as will fit to the new allocation, frees the old allocation, and returns a pointer to the allocated memory.
This is pretty much exactly what you are doing, but you can let the library handle it for you.
(May I also humbly suggest using the word "focal" slightly less to name variables in your function?) (Also also, I'm not really clear on why focalPoints in your struct is a pointer-to-pointer. You just want an array of structs -- a single pointer should be fine.)
Consider the following (somewhat extensive) rewrite; hope that it's helpful in some way.
typedef struct{
CGPoint *points; // Single pointer
NSUInteger count;
CGRect boundingRect;
} FocalPoints;
// Renamed to match Apple's style, like e.g. CGRectIntersectsRect()
void FocalPointsAddPoint (FocalPoints *, CGPoint);
void FocalPointsAddPoint (FocalPoints *f, CGPoint thePoint){
if (thePoint.x == CGFLOAT_MAX) return;
if (!CGRectContainsPoint(f->boundingRect, thePoint)) return;
NSUInteger origCount = f->count; // |count| is typed as NSUInteger; |origCount|
NSUInteger newCount = origCount + 1; // and |newCount| should be consistent
// Greatly simplified by using realloc()
f->points = (CGPoint *) realloc(f->points, newCount * sizeof(CGPoint));
(f->points)[newCount-1] = thePoint;
f->count = newCount;
}
int main(int argc, const char * argv[])
{
#autoreleasepool {
// Just for testing; any point should be inside this rect
CGRect maxRect = CGRectMake(0, 0, CGFLOAT_MAX, CGFLOAT_MAX);
// Can initialize |points| to NULL; both realloc() and free() know what to do
FocalPoints fp = (FocalPoints){NULL, 0, maxRect};
int i;
for( i = 0; i < 10; i++ ){
FocalPointsAddPoint(&fp, CGPointMake(arc4random() % 100, arc4random() % 100));
NSLog(#"%#", NSStringFromPoint(fp.points[i]));
}
}
return 0;
}
I think my algorithm has flawed logic somewhere. Calling the two functions should return the same image however it doesn't! Can anyone see where my logic goes wrong?
These functions are used on PNG-images, I have found that they store colors as follows: ALPHA, RED, GREEN, BLUE. Repeatingly for the whole image. "pixels" is just a long array of those values (like a list).
My intent is to do a lowpass filter on the image, which is a lot easier logic if you instead use a two dimentional array / matrix of the image.
// loading pixels
UIImage *image = imageView.image;
CGImageRef imageRef = image.CGImage;
NSData *data = (NSData *)CGDataProviderCopyData(CGImageGetDataProvider(imageRef));
char *pixels = (char *)[data bytes];
// editing image
char** matrix = [self mallocMatrix:pixels withWidth:CGImageGetWidth(imageRef) andHeight:CGImageGetHeight(imageRef)];
char* newPixels = [self mallocMatrixToList:matrix withWidth:CGImageGetWidth(imageRef) andHeight:CGImageGetHeight(imageRef)];
pixels = newPixels;
and the functions looks like this:
- (char**)mallocMatrix:(char*)pixels withWidth:(int)width andHeight:(int)height {
char** matrix = malloc(sizeof(char*)*height);
int c = 0;
for (int h=0; h < height; h++) {
matrix[h] = malloc(sizeof(char)*width*4);
for (int w=0; w < (width*4); w++) {
matrix[h][w] = pixels[c];
c++;
}
}
return matrix;
}
- (char*)mallocMatrixToList:(char**)matrix withWidth:(int)width andHeight:(int)height {
char* pixels = malloc(sizeof(char)*height*width*4);
int c = 0;
for (int h=0; h < height; h++) {
for (int w=0; w < (width*4); w++) {
pixels[c] = matrix[h][w];
c++;
}
}
return pixels;
}
Edit: Fixed the malloc as posters pointed out. Simplified the algorithm a bit.
I have not tested your code but it appears you are allocating the incorrect size for your matrix and low pass filter as well as not moving to the next pixel correctly.
- (char**) mallocMatrix:(char*)pixels withWidth:(int)width andHeight:(int)height {
//When using Objective-C do not cast malloc (only do so with Objective-C++)
char** matrix = malloc(sizeof(char*)*height);
for (int h=0; h < height; h++) {
//Each row needs to malloc the sizeof(char) not char *
matrix[h] = malloc(sizeof(char)*width*4);
for (int w=0; w < width; w++) {
// Varje pixel har ARGB
for (int i=0; i < 4; i++) {
matrix[h][w+i] = pixels[h*w+i];
}
}
}
return matrix;
}
- (char*) mallocLowPassFilter:(char**)matrix withWidth:(int)width andHeight:(int)height
{
//Same as before only malloc sizeof(char)
char* pixels = malloc(sizeof(char)*height*width*4);
for (int h=0; h < height; h++) {
for (int w=0; w < width; w++) {
// Varje pixel har ARGB
for (int i=0; i < 4; i++) {
// TODO: Lowpass here
pixels[h*w+i] = matrix[h][w+i];
}
}
}
return pixels;
}
Note: This code, as you know, is limited to ARGB images. If you would like to support more image formats there are additional functions available to get more information about your image such as CGImageGetColorSpace to find the pixel format (ARGB, RGBA, RGB, etc...), and CGImageGetBytesPerRow to get the number of bytes per row (you wouldn't have to multiply width by channels per pixel).
In my h file I declare a var that later should be an array:
#interface myClass : CCNode {
CGPoint *mVertices;
}
#end
In my init method:
mVertices = malloc(size * size * sizeof(CGPoint));
mVertices[0][0] = ccp(0,0);
At this last line I get an error Subscripted value is neither array nor pointer.
Why do I get this error and how to solve that problem?
mVertices is a pointer, but you treat it like a two-dimensional array which is not allowed (you may treat it like a one-dimensional array, though).
Creating a dynamic multi-dimensional array in (Objective)-C is tricky insofar as the compiler would need to know the size of all but the first dimension to actually compile where in memory the element is situated.
But you can do the calculation yourself:
mVertices[(row * size) + column] = ccp(row, column);
You might want to define a macro for that:
#define VERTICE_ACCESS(row,colum) mVertices[(row * size) + column]
Your array is not two dimensional. It's just a list of vertices.
If you want to allocate space for a dynamic two dimensional array in C you could do:
CGPoint** mVertices;
NSInteger nrows = 10;
NSInteger ncolumns = 5;
mVertices = calloc(sizeof(CGPoint*), nrows);
if(mVertices == NULL){NSLog(#"Not enough memory to allocate array.");}
for(NSUInteger i = 0; i < nrows; i++)
{
mVertices[i] = calloc(sizeof(CGPoint), ncolumns);
if(mVertices[i] == NULL){NSLog(#"Not enough memory to allocate array.");}
}
mVertices[0][5] = CGPointMake(12.0, 24.0);
mVertices[1][5] = CGPointMake(22.0, 24.0);
mVertices[2][5] = CGPointMake(32.0, 24.0);
mVertices[2][1] = CGPointMake(32.0, 24.0);
for(NSUInteger i = 0; i < nrows; i++)
{
for (int k = 0; k < ncolumns; k++)
{
NSLog(#"Point %#", NSStringFromPoint(NSPointFromCGPoint(mVertices[i][k])));
}
}
I used calloc instead of malloc to get CGPoints initialized with 0.0.