Rotate text with transformations

JurekGP

I want to rotate some string and I'm wondering how I can do it best. I found this topic: https://www.allegro.cc/forums/thread/605671
So, how we can see there are two options. Draw to another bitmap, or use transformations.
On begin, I thought that draw to another bitmap will be easier, but I haven't done it before. Next I found example ex_transform.c, on this page, and I tried with it.
I commented what I don't need now, and wrote something like this: http://wklej.org/id/1762201/

Because transformations are for me completly new component, I don't know exactly what I do, so I can't control this. I've never drawn on two different buffers before. Sample text is drawing about this 90 degress what I want in my destination project.
But why my sample bitmap is cut which I draw in 177th line? I guess this is about drawing on two others buffers. First physically "buffer", and second this is bitmap "overlay".
These three lines (175-177) are correct? I think no, because I wrote coordinates (20, 20), but they are bigger...

Maybe easier will be draw this text to another bitmap, and then just rotate it?

Edgar Reynaldo

To use a transform you would probably only need a rotation and a translation transform, like so :

#SelectExpand
  1ALLEGRO_TRANSFORM t;
  2al_identity_transform(&t);
  3
  4const char* str = "MyRotatedString";
  5
  6int tw = al_get_text_width(font , str);
  7int th = al_get_font_line_height(font);
  8
  9// center x and y for text destination
 10int cx = 400;
 11int cy = 300;
 12
 13al_rotate_transform(&t , M_PI/2.0f);
 14al_translate_transform(&t , cx , cy);
 15
 16al_use_transform(&t);
 17al_draw_textf(font , al_map_rgba(255,255,255,255) , 0 , 0 , ALLEGRO_ALIGN_CENTER,
 18              "%s" , str);

jmasterx

I ended up doing:

  int GraphicsContext::drawRotatedText( const std::string& text,agui::Font* font,const agui::Color& color, int x, int y, float deg, int flags )
  {
    int fx = font->getTextWidth(text) / 2;
    int fy = font->getLineHeight() / 2;
    m_transform.identity();
    m_transform.translate(-fx,-fy);
    m_transform.rotate(deg);
    m_transform.translate(x,y);
    useTransform(m_transform);
    drawText(text,font,color,0,0,flags);
    resetTransform();
    return fx * 2;
  }

Taken from my GraphicsContext:

#SelectExpand
   1#include "Game/Engine/GraphicsContext.hpp"
   2#include "Agui/Backends/Allegro5/Allegro5Font.hpp"
   3
   4namespace cge
   5{
GraphicsContext::GraphicsContext(void)
  :m_shader(NULL),m_tripleBuffer(false),
  m_buffer(NULL),m_needsFlip(false)
{
  black = al_map_rgb(0,0,0);
}
  12
GraphicsContext::~GraphicsContext(void)
{
  if(m_buffer)
  {
    delete m_buffer;
    m_buffer = NULL;
  }
}
  21
void GraphicsContext::drawSprite( Sprite* sprite, float x, float y, int flags )
{
  al_draw_bitmap(sprite->getBitmap(),x,y,flags);
}
  26
void GraphicsContext::drawTintedSprite( Sprite* sprite, const Color& tint, float x, float y, int flags )
{
  al_draw_tinted_bitmap(sprite->getBitmap(),tint.getColor(),x,y,flags);
}
  31
void GraphicsContext::drawSpriteRegion( Sprite* sprite, float sourceX, float sourceY, float sourceWidth, float sourceHeight, float x, float y, int flags )
{
  al_draw_bitmap_region(
    sprite->getBitmap(),
    sourceX,
    sourceY,
    sourceWidth,
    sourceHeight,
    x,
    y,
    flags);
}
  44
void GraphicsContext::drawTintedSpriteRegion( Sprite* sprite,const Color& tint, float sourceX, float sourceY, float sourceWidth, float sourceHeight, float x, float y, int flags )
{
  al_draw_tinted_bitmap_region(
    sprite->getBitmap(),
    tint.getColor(),
    sourceX,
    sourceY,
    sourceWidth,
    sourceHeight,
    x,
    y,
    flags);
}
  58
void GraphicsContext::drawRotatedSprite( Sprite* sprite, float centerX, float centerY, float x, float y, float radAngle, int flags )
{
  al_draw_rotated_bitmap(
    sprite->getBitmap(),
    centerX,
    centerY,
    x,
    y,
    radAngle,
    flags);
}
  70
void GraphicsContext::drawTintedRotatedSprite( Sprite* sprite, const Color& tint, float centerX, float centerY, float x, float y, float radAngle, int flags )
{
  al_draw_tinted_rotated_bitmap(
    sprite->getBitmap(),
    tint.getColor(),
    centerX,
    centerY,
    x,
    y,
    radAngle,
    flags);
}
  83
void GraphicsContext::drawScaledRotatedSprite( Sprite* sprite, float centerX, float centerY, float x, float y, float xScale, float yScale, float radAngle, int flags )
{
  al_draw_scaled_rotated_bitmap(
    sprite->getBitmap(),
    centerX,
    centerY,
    x,
    y,
    xScale,
    yScale,
    radAngle,
    flags);
}
  97
void GraphicsContext::drawTintedScaledRotatedSprite( Sprite* sprite, const Color& tint, float centerX, float centerY, float x, float y, float xScale, float yScale, float radAngle, int flags )
{
  al_draw_tinted_scaled_rotated_bitmap(
    sprite->getBitmap(),
    tint.getColor(),
    centerX,
    centerY,
    x,
    y,
    xScale,
    yScale,
    radAngle,
    flags);
}
 112
void GraphicsContext::drawScaledSprite( Sprite *sprite, float sourceX, float sourceY, float sourceWidth, float sourceHeight, float x, float y, float destinationWidth, float destinationHeight, int flags )
{
  al_draw_scaled_bitmap(
    sprite->getBitmap(),
    sourceX,
    sourceY,
    sourceWidth,
    sourceHeight,
    x,
    y,
    destinationWidth,
    destinationHeight,
    flags
    );
}
 128
void GraphicsContext::clear()
{
  al_clear_to_color(black);
}
 133
void GraphicsContext::clear( const Color& color )
{
  al_clear_to_color(color.getColor());
}
 138
void GraphicsContext::clearTransparent()
{
  al_clear_to_color(al_map_rgba(0,0,0,0));
}
 143
void GraphicsContext::setTarget( Sprite* sprite )
{
  al_set_target_bitmap(sprite->getBitmap());
}
 148
void GraphicsContext::setTargetToBackbuffer()
{
  al_set_target_bitmap(al_get_backbuffer(al_get_current_display()));
}
 153
void GraphicsContext::holdDrawing()
{
  al_hold_bitmap_drawing(true);
}
 158
void GraphicsContext::unholdDrawing()
{
  al_hold_bitmap_drawing(false);
}
 163
void GraphicsContext::flipDisplay()
{
    m_needsFlip = true;
  
}
 169
void GraphicsContext::setClippingRect( int x, int y, int w, int h )
{
  al_set_clipping_rectangle(x,y,w,h);
}
 174
void GraphicsContext::getClippingRect( int&x,int&y,int&w,int&h )
{
  al_get_clipping_rectangle(&x,&y,&w,&h);
}
 179
void GraphicsContext::drawTintedScaledSprite( Sprite *sprite,const Color & color, float sourceX, float sourceY, float sourceWidth, float sourceHeight, float x, float y, float destinationWidth, float destinationHeight, int flags )
{
  al_draw_tinted_scaled_rotated_bitmap(sprite->getBitmap(),
    color.getColor(),sourceWidth / 2, sourceHeight / 2,x + (destinationWidth / 2),y + (destinationHeight / 2),destinationWidth / (float)sourceWidth,destinationHeight / (float)sourceHeight,0.0f,0);
}
 185
void GraphicsContext::drawText( 
  const std::string& text,Font* font,const Color& color, int x, int y, int flags )
{
  al_draw_text(font->getFont(),
    color.getColor(),
    x,y,flags,text.c_str());
}
 193
void GraphicsContext::drawText( 
  const std::string& text,agui::Font* font,const agui::Color& color, int x, int y, int flags )
{
  al_draw_text(((agui::Allegro5Font*)font)->getFont(),
    al_map_rgba_f(color.getR(),color.getG(),color.getB(),color.getA()),
    x,y,flags,text.c_str());
}
 201
void GraphicsContext::drawFilledRectangle( int x, int y, int w, int h,const agui::Color& color )
{
  al_draw_filled_rectangle(x,y,x + w,y + h,al_map_rgba_f(color.getR(),color.getG(),color.getB(),color.getA()));
}
 206
void GraphicsContext::setShader( Shader* shader )
{
  m_shader = shader;
}
 211
void GraphicsContext::resetTransform()
{
  ALLEGRO_TRANSFORM t;
  al_identity_transform(&t);
  al_use_transform(&t);
}
 218
void GraphicsContext::useTransform( Transformation& t )
{
  al_use_transform(&t.getTransform());
}
 223
int GraphicsContext::drawRotatedText( const std::string& text,agui::Font* font,const agui::Color& color, int x, int y, float deg, int flags )
{
  int fx = font->getTextWidth(text) / 2;
  int fy = font->getLineHeight() / 2;
  m_transform.identity();
  m_transform.translate(-fx,-fy);
  m_transform.rotate(deg);
  m_transform.translate(x,y);
  useTransform(m_transform);
  drawText(text,font,color,0,0,flags);
  resetTransform();
  return fx * 2;
}
 237
void GraphicsContext::begin()
{
  if(isBuffering())
  {
    resetTransform();
  }
  
}
 246
void GraphicsContext::resizeBuffer(int w, int h)
{
  if(isBuffering())
  {
    delete m_buffer;
    m_buffer = new Sprite(w,h);
  }
}
 255
bool GraphicsContext::isBuffering() const
{
  return m_tripleBuffer;
}
 260
void GraphicsContext::setBuffering( bool buffering )
{
  m_tripleBuffer = buffering;
  delete m_buffer;
  m_buffer = NULL;
 266
  if(buffering)
  {
    resizeBuffer(al_get_display_width(al_get_current_display())
      ,al_get_display_height(al_get_current_display()));
  }
}
 273
void GraphicsContext::end()
{
  if(m_needsFlip)
  {
    m_needsFlip = false;
    al_flip_display();
  }
  
}
 283
void GraphicsContext::setTargetToBuffer()
{
  setTarget(m_buffer);
}
 288
Sprite* GraphicsContext::getBuffer()
{
  return m_buffer;
}
 293}

and Transformation:

#SelectExpand
  1Transformation::Transformation(void)
  2{
  3  identity();
  4}
  5
  6Transformation::~Transformation(void)
  7{
  8}
  9
 10ALLEGRO_TRANSFORM& Transformation::getTransform()
 11{
 12  return m_transform;
 13}
 14
 15void Transformation::identity()
 16{
 17  al_identity_transform(&m_transform);
 18}
 19
 20void Transformation::translate( float x, float y )
 21{
 22  al_translate_transform(&m_transform,x,y);
 23}
 24
 25void Transformation::rotate( float deg )
 26{
 27  al_rotate_transform(&m_transform,deg);
 28}
 29
 30void Transformation::scale( float x, float y )
 31{
 32  al_scale_transform(&m_transform,x,y);
 33}

Edgar Reynaldo

Minor correction to what I posted above :

al_draw_textf(font , al_map_rgba(255,255,255,255) , 0 , -al_get_font_line_height(font)/2.0 , ALLEGRO_ALIGN_CENTER, "%s" , str);

Just to center the text vertically as well, since allegro doesn't do that.

JurekGP

Thanks you both! Now I'm correctly rotating this text how I want.
Edgar Reynaldo
Your simply example was very helpful.
jmasterx
Your code let me do it in one, valid detail. Agui API is very interesting. When I will have time, I try it.

But in my destination project this text is piece of something what is scrolling. So I must scale it too. In local y axis.
Until now, to testing, I had just bitmap and scrolling was very easy. I don't know how I can use function al_scale_transform(), so one more question. How I can scale this transformated string? I don't think so, just one line with this said function, will be all.

1. normal state

2. when is scrolling

anto80

Allegro 5 manual said:

The transformations are combined in the order of the function invocations. Thus to create a transformation that first rotates a point and then translates it, you would (starting with an identity transformation) call al_rotate_transform and then al_translate_transform. This approach is opposite of what OpenGL uses but similar to what Direct3D uses.

al_identity_transform(&T);
al_rotate_transform(....)
al_scale_transform(&T, 2, 2);
al_translate_transform(&T, 100, 0);
al_use_transform(T);

You may also look at this thread: https://www.allegro.cc/forums/thread/614764

Thread #615586. Printed from Allegro.cc