Rotate text with transformations

Rotate text with transformations

JurekGP

Member #15,891

February 2015

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?

Hi! I'm Pole and my english is not very well. So, please understanding to me. :)

Edgar Reynaldo

Major Reynaldo

May 2007

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);

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jmasterx

Member #11,410

October 2009

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}

Agui GUI API -> https://github.com/jmasterx/Agui
Agui 0.2 Release Thread -> https://www.allegro.cc/forums/thread/612830

Edgar Reynaldo

Major Reynaldo

May 2007

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

Member #15,891

February 2015

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

Hi! I'm Pole and my english is not very well. So, please understanding to me. :)

anto80

Member #3,230

February 2003

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

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