Advanced Drawing Functions

Advanced drawing functions

Above, a number of basic drawing functions have been described. Here you find a number of additional functions that offer you a lot more possibilities. First of all there are functions to draw shapes with gradient colors. Secondly there are functions to draw more general polygons, and finally there is the possibility to draw texture mapped polygons.

The following extended versions of the basic drawing functions exist. each of them gets extra color parameters that are used the determine the color at different vertices. The standard drawing color is not used in these functions.

draw_point_color(x,y,col1) Draws a point at (x,y) in the given color.
draw_line_color(x1,y1,x2,y2,col1,col2) Draws a line from (x1,y1) to (x2,y2), interpolating the color between col1 and col2.
draw_line_width_color(x1,y1,x2,y2,w,col1,col2) Draws a line from (x1,y1) to (x2,y2) with width w interpolating the color between col1 and col2.
draw_rectangle_color(x1,y1,x2,y2,col1,col2,col3,col4,outline) Draws a rectangle. The four colors indicated the colors at the top-left, top-right, bottom-right, and bottom-left vertex. outline indicates whether only the outline must be drawn (true) or it should be filled (false).
draw_roundrect_color(x1,y1,x2,y2,col1,col2,outline) Draws a rounded rectangle. col1 is the color in the middle and col2 the color at the boundary. outline indicates whether only the outline must be drawn (true) or it should be filled (false).
draw_triangle_color(x1,y1,x2,y2,x3,y3,col1,col2,col3,outline) Draws a triangle. The three colors are the colors of the three vertices which is interpolated over the triangle. outline indicates whether only the outline must be drawn (true) or it should be filled (false).
draw_circle_color(x,y,r,col1,col2,outline) Draws a circle at (x,y) with radius r. col1 is the color in the middle and col2 the color at the boundary. outline indicates whether only the outline must be drawn (true) or it should be filled (false).
draw_ellipse_color(x1,y1,x2,y2,col1,col2,outline) Draws an ellipse. col1 is the color in the middle and col2 the color at the boundary. outline indicates whether only the outline must be drawn (true) or it should be filled (false).

You can also draw larger primitives. This works slightly different. You begin by specifying the primitive you want to draw. Next you specify the vertices for it, and finally you end the primitive, at which moment it is drawn. There are six types of primitives:

pr_pointlist The vertices are a set of points.
pr_linelist The vertices are a set of line segments. Each pair of vertices forms a line segment. So there must be an even set of vertices.
pr_linestrip The vertices form a polyline with the first connected to the second, the second to the third, etc. The last one is not connected to the first one. You have to specify an extra copy of the first vertex for this.
pr_trianglelist The vertices are a set of triangles. Each triple of vertices forms a triangle. So the number of vertices must be a multiple of 3.
pr_trianglestrip The vertices again form triangles but this time it works slightly different. The first three form the first triangle. The last two of these vertices, together with the next vertex, form the second triangle, etc. So each new vertex specifies a new triangle, connected to the previous one.
pr_trianglefan Similar to a triangle list but this time the first vertex is part of all the triangles. Again, each new vertex specifies a new triangle, connected to the previous vertex and the first vertex.

The following functions exist for drawing primitives

draw_primitive_begin(kind) Start a primitive of the indicated kind.
draw_vertex(x,y) Add vertex (x,y) to the primitive, using the color and alpha value set before.
draw_vertex_color(x,y,col,alpha) Add vertex (x,y) to the primitive, with its own color and alpha value. This allows you to create primitives with smoothly changing color and alpha values.
draw_primitive_end() End the description of the primitive. This function actually draws it.

Finally, it is possible to draw primitives using sprites or backgrounds as textures. When using a texture the image is placed on the primitive, reshaping it to fit the primitive. Textures are used to add detail to primitives, e.g. a brick wall. To use textures you first must obtain the id of the texture you want to use. For this the following functions exist:

sprite_get_texture(spr,subimg) Returns the id of the texture corresponding to subimage subimg of the indicated sprite.
background_get_texture(back) Returns the id of the texture corresponding to the indicated background.

A selected texture might not yet be in video memory. The system will put it there once you need it but sometimes you want to decide this yourself. For this the following two functions exist:

texture_preload(texid) Puts the texture immediately into video memory.
texture_set_priority(texid,prio) When there is too little video memory some will be removed temporarily to make room for others that are needed. The ones with lowest priority are removed first. Default, all have priority 0 but you can change the priority here. (Use positive values!)

To add textures to primitives you must specify which parts of the textures must be put where on the primitive. Positions in the texture are indicated with values between 0 and 1 but there is a problem here. Sizes of textures must be powers of 2 (so e.g. 32x32 or 64x64). If you want to use sprites or background as textures you better make sure they have such a size. If not, the test will be blank. To find out which part of the texture is actually used you can use the following two functions. They return a value between 0 and 1 that indicates the width or height of the actual part of the texture being used. Specifying this value as texture coordinate will indicate the right or bottom side of the texture.

texture_get_width(texid) Returns the width of the texture with the given id. The width lies in the range 0-1.
texture_get_height(texid) Returns the height of the texture with the given id. The height lies in the range 0-1.

To draw textured primitives you use the following functions:

draw_primitive_begin_texture(kind,texid) Start a primitive of the indicated kind with the given texture.
draw_vertex_texture(x,y,xtex,ytex) Add vertex (x,y) to the primitive with position (xtex,ytex) in the texture, blending with the color and alpha value set before. xtex and ytex should normally lie between 0 and 1 but also larger values can be used, leading to a repetition of the texture (see below).
draw_vertex_texture_color(x,y,xtex,ytex,col,alpha) Add vertex (x,y) to the primitive with position (xtex,ytex) in the texture, blending with its own color and alpha value.
draw_primitive_end() End the description of the primitive. This function actually draws it.

There are three functions that influence how textures are drawn:

texture_set_interpolation(linear) Indicates whether to use linear interpolation (true) or pick the nearest pixel (false). Linear interpolation gives smoother textures but can also be a bit blurry and sometimes costs extra time. This setting also influence the drawing of sprites and background. Default is false. (This can also be changed in the global game settings.)
texture_set_blending(blend) Indicates whether to use blending with colors and alpha values. Switching this off might be faster on old hardware. This setting also influence the drawing of sprites and background. Default is true.
texture_set_repeat(repeat) Indicates whether to use repeat the texture. This works as follows. As indicated above texture coordinates lie in the range 0-1. If you specify a value larger than 1, default the rest is not drawn. By setting repeat to true the texture is repeated. Note that sprites and backgrounds are always drawn without repeating. So once you draw a sprite of background this value is reset to false. Default is false.

There are two more function that are not only useful for drawing textures. Normally primitives are blended with the background using the alpha value. You can actually indicate how this must happen. Besides the normal mode it is possible to indicate that the new color must be added to the existing color or subtracted from the existing color. This can be used to create e.g. spot lights or shadows. Also it is possible to sort of take the maximum of the new and existing color. This can avoid certain saturation effects that you can get with adding. Note that both subtracting and maximum do not take the alpha value fully into account. (DirectX does not allow this.) So you better make sure the outside area is black. There are two functions. The first one only gives you the four options described above. The second function gives you a lot more possibilities. You should experiment a bit with the settings. If used effectively they can be used to create e.g. interesting explosion or halo effects.

draw_set_blend_mode(mode) Indicates what blend mode to use. The following values are possible: bm_normal, bm_add, bm_subtract, and bm_max. Don't forget to reset the mode to normal after use because otherwise also other sprites and even the backgrounds are drawn with the new blend mode.
draw_set_blend_mode_ext(src,dest) Indicates what blend mode to use for both the source and destination color. The new color is some factor times the source and another factor times the destination. These factors are set with this function. To understand this, the source and destination both have a red, green, blue, and alpha component. So the source is (Rs, Gs, Bs, As) and the destination is (Rd, Gd, Bd, Ad). All are considered to lie between 0 and 1. The blend factors you can choose for source and destination are:

• bm_zero: Blend factor is (0, 0, 0, 0).
• bm_one: Blend factor is (1, 1, 1, 1).
• bm_src_color: Blend factor is (Rs, Gs, Bs, As).
• bm_inv_src_color: Blend factor is (1–Rs, 1–Gs, 1–Bs, 1–As).
• bm_src_alpha: Blend factor is (As, As, As, As).
• bm_inv_src_alpha: Blend factor is (1–As, 1–As, 1–As, 1–As).
• bm_dest_alpha: Blend factor is (Ad, Ad, Ad, Ad).
• bm_inv_dest_alpha: Blend factor is (1–Ad, 1–Ad, 1–Ad, 1–Ad).
• bm_dest_color: Blend factor is (Rd, Gd, Bd, Ad).
• bm_inv_dest_color: Blend factor is (1–Rd, 1–Gd, 1–Bd, 1–Ad).
• bm_src_alpha_sat: Blend factor is (f, f, f, 1); f = min(As, 1–Ad).

For example, the normal blending mode sets the source blending to bm_src_alpha and the destination blending to bm_inv_src_alpha. Don't forget to reset the mode to normal after use because otherwise also other sprites and even the backgrounds are drawn with the new blend mode.

Drawing texture primitives is a bit of work but can lead to great results. You can even use it to make fake 3D games.