SDL provides several ways to draw on screen; these methods can be broken down into: Primitives, Images and Text. All three methods draw on a single object the Surface. The Surface is represented by SDLx::Surface. Even our SDLx::App is a SDLx::Surface. This means that we can draw directly on the SDLx::App, however there are several advantages to drawing on multiple surfaces. In this chapter we will explore these methods of drawing, and make a pretty picture.
use SDL;
use SDLx::App;
my $app = SDLx::App->new( w => 400, h => 400, title => 'Drawing Examples' );
#Draw Code Starts Here
#Draw Code Ends Here
$app->update();
sleep(2);Drawing in SDL are done on Surfaces. The SDLx::Surface object provides access to methods in the form of:
$surface->draw_{something}( .... );Parameters are usually provided as array references, to define areas and colors.
Some parameters are just a quick definition of the positions and dimensions. For a rectangle that will be placed at (20, 20) pixel units on the screen, and a dimension of 40x40 pixel units the following would suffice.
my $rect = [20, 20, 40, 40];in SDL is described by 4 numbers. The first three numbers define the Red, Blue, Green intensity of the color. The final number defines the transparency of the Color.
my $color = [255, 255, 255, 255];The values of the numbers range from 0-255 for 32 bit depth in RGBA format.
Drawing are usually simples shapes that can be used for creating graphics dynamically.
$app->draw_line( [200,20], [20,200], [255, 255, 0, 255] );This will draw a yellow line from positions (200,20) to (20,200) .
Rectangles are a common building blocks for games. In SDL rectangles are the most cost effective of the primitives to draw.
$app->draw_rect( [10,20, 40, 40 ], [255, 255, 255,255] );The above will add a white square of size 40x40 onto the screen at the position (10,20).
Circles are drawn similarly either filled or unfilled.
$app->draw_circle( [100,100], 20, [255,0,0,255] );
$app->draw_circle_filled( [100,100], 19, [0,0,255,255] );Now we will have a filled circle, colored blue and unfilled circle, colored as red.
For more complex drawing functions have a look at SDL::GFX::Primitives.
Now we don't always use one surface. Most games use many Surfaces. These are held in memory. You can make blank ones and draw on them. Or you can make Surfaces from various data.
Images can be loaded as surfaces.
Sprites is a lot better way to think of this.
It is ugly but can be useful.
This is probably the more common way to use text in SDL. However it has its limitations
Pango features several rendering options, and thus is heavy. It is good for multilingual support.
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