You're right about that. Yet, ironically, doing it the right way brings worst results! Now the image never faces the direction it's going! What's going on? O_o

Do you still have any of the 'corrective' code in place? That is, are you modifying the angle returned by atan2() in any way?

Also, although this is probably too obvious, are you missing any degrees<->radians conversions anywhere?

Yes, correcting the order of the parameters in the atan2 function, the code that rotates the image is ***exactly*** this one:

[source lang="cpp"]void rotate(){ float radians = atan2(y_vel, x_vel); //0; //1.5708; // if (x_vel<0) { radians = 0-(3.1416-atan2(y_vel,x_vel)); } float cosine=(float)cos(radians); float sine=(float)sin(radians); int bmp_width = image.get_width(); int bmp_height = image.get_height(); float point1_x=(-bmp_height*sine); float point1_y=(bmp_height*cosine); float point2_x=(bmp_width*cosine-bmp_height*sine); float point2_y=(bmp_height*cosine+bmp_width*sine); float point3_x=(bmp_width*cosine); float point3_y=(bmp_width*sine); float minx=min(0,min(point1_x,min(point2_x,point3_x))); float miny=min(0,min(point1_y,min(point2_y,point3_y))); float maxx=max(point1_x,max(point2_x,point3_x)); float maxy=max(point1_y,max(point2_y,point3_y)); int dest_width=(int)ceil(fabs(maxx)-minx); int dest_height=(int)ceil(fabs(maxy)-miny); if (image_rotated.buffer.size()!= (uint32_t)dest_width*dest_height) { image_rotated.new_transparent(dest_width, dest_height); } for(int x=0;x<dest_width;x++) { for(int y=0;y<dest_height;y++) { int src_bitmap_x=(int)((x+minx)*cosine+(y+miny)*sine); int src_bitmap_y=(int)((y+miny)*cosine-(x+minx)*sine); if( src_bitmap_x>=0 && src_bitmap_x<image.get_width() && src_bitmap_y>=0 && src_bitmap_y<image.get_height() ) { image_rotated.buffer[y * image_rotated.get_width() + x] = image.buffer[src_bitmap_x * image.get_width() + src_bitmap_y]; } } }}[/source]

Given that code, now the image never faces towards the direction it's going... I still think I should cap the rotation to 180º if I flip the image before rotating it. Yet I'm not sure how to limit it... As far as I can tell everything seems to work in radians here... *blocked*

EDIT: If I change the order of the parameters in the atan2 function to be as they should (y, x) and I swap the sin and cos then it works exactly as having the atan2 function with the parameters as (x,y).

float cosine=(float)sin(radians);
float sine=(float)cos(radians);

You shouldn't need to cap the rotation, xvel<0 should always result in a rotation between pi/2 and 3pi/2 (90-270 degrees) while xvel > 0 results in one that is either between 0 and pi/2(0-90 degrees) or between 3pi/2 and 2pi (270-360 degrees)

The fact that your image gets rotated at all when the angle is 0 means that you've messed up your rotation formula. (when radians is 0 there should be no rotation)

//some mindless typing to help me keep my mind on track, possible conclusion further down.

sin(0) = 0

cos(0) = 1

Thus your 3 points when you're not supposed to rotate anything becomes:

float point1_x=0;float point1_y=bmp_height;

float point2_x=bmp_width;float point2_y=bmp_height;

float point3_x=bmp_width;float point3_y=0;

then:

float minx=min(0,min(point1_x,min(point2_x,point3_x)));float miny=min(0,min(point1_y,min(point2_y,point3_y)));float maxx=max(point1_x,max(point2_x,point3_x));float maxy=max(point1_y,max(point2_y,point3_y));

minx = 0

miny = 0

maxx = bmp_width

maxy = bmp_height

//Image size doesn't change atleast.

Then for each pixel in the rotated image you do

int src_bitmap_x=(int)((x+0));
int src_bitmap_y=(int)((y+0));
if( src_bitmap_x>=0 && src_bitmap_x<image.get_width() && src_bitmap_y>=0 && src_bitmap_y<image.get_height() ) {
image_rotated.buffer[y * image_rotated.get_width() + x] = image.buffer[src_bitmap_x * image.get_width() + src_bitmap_y];
}

shouldn't:

image_rotated.buffer[y * image_rotated.get_width() + x] = image.buffer[

**src_bitmap_x * image.get_width() + src_bitmap_y**];

be

image_rotated.buffer[y * image_rotated.get_width() + x] = image.buffer[

**src_bitmap_y * image.get_width() + src_bitmap_x**];