Rendering API documentation

Version: stable

Rendering functions, messages and constants. The "render" namespace is accessible only from render scripts.

The rendering API is built on top of OpenGL ES 2.0, is a subset of the OpenGL computer graphics rendering API for rendering 2D and 3D computer graphics. OpenGL ES 2.0 is supported on all our target platforms.

It is possible to create materials and write shaders that require features not in OpenGL ES 2.0, but those will not work cross platform.

Functions

render.clear()

render.clear(buffers)

Clear buffers in the currently enabled render target with specified value.

PARAMETERS

EXAMPLES

Clear the color buffer and the depth buffer.

render.clear({[render.BUFFER_COLOR_BIT] = vmath.vector4(0, 0, 0, 0), [render.BUFFER_DEPTH_BIT] = 1})

render.constant_buffer()

render.constant_buffer()

Constant buffers are used to set shader program variables and are optionally passed to the render.draw() function. The buffer's constant elements can be indexed like an ordinary Lua table, but you can't iterate over them with pairs() or ipairs().

PARAMETERS

RETURNS

EXAMPLES

Set a "tint" constant in a constant buffer in the render script:

local constants = render.constant_buffer()
constants.tint = vmath.vector4(1, 1, 1, 1)

Then use the constant buffer when drawing a predicate:

render.draw(self.my_pred, constants)

render.delete_render_target()

render.delete_render_target(render_target)

Deletes a previously created render target.

PARAMETERS

EXAMPLES

How to delete a render target:

 render.delete_render_target(self.my_render_target)

render.disable_material()

render.disable_material()

If a material is currently enabled, disable it.

The name of the material must be specified in the ".render" resource set in the "game.project" setting.

PARAMETERS

EXAMPLES

Enable material named "glow", then draw my_pred with it.

render.enable_material("glow")
render.draw(self.my_pred)
render.disable_material()

render.disable_state()

render.disable_state(state)

Disables a render state.

PARAMETERS

EXAMPLES

Disable face culling when drawing the tile predicate:

render.disable_state(render.STATE_CULL_FACE)
render.draw(self.tile_pred)

render.disable_texture()

render.disable_texture(unit)

Disables a texture unit for a render target that has previourly been enabled.

PARAMETERS

EXAMPLES

function update(self, dt)
    render.enable_texture(0, self.my_render_target, render.BUFFER_COLOR_BIT)
    -- draw a predicate with the render target available as texture 0 in the predicate
    -- material shader.
    render.draw(self.my_pred)
    -- done, disable the texture
    render.disable_texture(0)
end

render.draw()

render.draw(predicate,[constants])

Draws all objects that match a specified predicate. An optional constant buffer can be provided to override the default constants. If no constants buffer is provided, a default system constants buffer is used containing constants as defined in materials and set through *.set_constant() and *.reset_constant() on visual components.

PARAMETERS

EXAMPLES

function init(self)
    -- define a predicate matching anything with material tag "my_tag"
    self.my_pred = render.predicate({hash("my_tag")})
end

function update(self, dt)
    -- draw everything in the my_pred predicate
    render.draw(self.my_pred)
end

Draw predicate with constant:

local constants = render.constant_buffer()
constants.tint = vmath.vector4(1, 1, 1, 1)
render.draw(self.my_pred, constants)

render.draw_debug3d()

render.draw_debug3d()

Draws all 3d debug graphics such as lines drawn with "draw_line" messages and physics visualization.

PARAMETERS

EXAMPLES

function update(self, dt)
    -- draw debug visualization
    render.draw_debug3d()
end

render.enable_material()

render.enable_material(material_id)

If another material was already enabled, it will be automatically disabled and the specified material is used instead.

The name of the material must be specified in the ".render" resource set in the "game.project" setting.

PARAMETERS

EXAMPLES

Enable material named "glow", then draw my_pred with it.

render.enable_material("glow")
render.draw(self.my_pred)
render.disable_material()

render.enable_state()

render.enable_state(state)

Enables a particular render state. The state will be enabled until disabled.

PARAMETERS

EXAMPLES

Enable stencil test when drawing the gui predicate, then disable it:

render.enable_state(render.STATE_STENCIL_TEST)
render.draw(self.gui_pred)
render.disable_state(render.STATE_STENCIL_TEST)

render.enable_texture()

render.enable_texture(unit,render_target,buffer_type)

Sets the specified render target's specified buffer to be used as texture with the specified unit. A material shader can then use the texture to sample from.

PARAMETERS

EXAMPLES

function update(self, dt)
    -- enable target so all drawing is done to it
    render.enable_render_target(self.my_render_target)

    -- draw a predicate to the render target
    render.draw(self.my_pred)

    -- disable target
    render.disable_render_target(self.my_render_target)

    render.enable_texture(0, self.my_render_target, render.BUFFER_COLOR_BIT)
    -- draw a predicate with the render target available as texture 0 in the predicate
    -- material shader.
    render.draw(self.my_pred)
end

render.get_height()

render.get_height()

Returns the logical window height that is set in the "game.project" settings. Note that the actual window pixel size can change, either by device constraints or user input.

PARAMETERS

RETURNS

EXAMPLES

Get the height of the window

local h = render.get_height()

render.get_render_target_height()

render.get_render_target_height(render_target,buffer_type)

Returns the specified buffer height from a render target.

PARAMETERS

RETURNS

EXAMPLES

-- get the height of the render target color buffer
local h = render.get_render_target_height(self.target_right, render.BUFFER_COLOR_BIT)

render.get_render_target_width()

render.get_render_target_width(render_target,buffer_type)

Returns the specified buffer width from a render target.

PARAMETERS

RETURNS

EXAMPLES

-- get the width of the render target color buffer
local w = render.get_render_target_width(self.target_right, render.BUFFER_COLOR_BIT)

render.get_width()

render.get_width()

Returns the logical window width that is set in the "game.project" settings. Note that the actual window pixel size can change, either by device constraints or user input.

PARAMETERS

RETURNS

EXAMPLES

Get the width of the window.

local w = render.get_width()

render.get_window_height()

render.get_window_height()

Returns the actual physical window height. Note that this value might differ from the logical height that is set in the "game.project" settings.

PARAMETERS

RETURNS

EXAMPLES

Get the actual height of the window

local h = render.get_window_height()

render.get_window_width()

render.get_window_width()

Returns the actual physical window width. Note that this value might differ from the logical width that is set in the "game.project" settings.

PARAMETERS

RETURNS

EXAMPLES

Get the actual width of the window

local w = render.get_window_width()

render.predicate()

render.predicate(tags)

This function returns a new render predicate for objects with materials matching the provided material tags. The provided tags are combined into a bit mask for the predicate. If multiple tags are provided, the predicate matches materials with all tags ANDed together.

The current limit to the number of tags that can be defined is 64.

PARAMETERS

RETURNS

EXAMPLES

Create a new render predicate containing all visual objects that have a material with material tags "opaque" AND "smoke".

local p = render.predicate({hash("opaque"), hash("smoke")})

render.render_target()

render.render_target(name,parameters)

Creates a new render target according to the supplied specification table.

The table should contain keys specifying which buffers should be created with what parameters. Each buffer key should have a table value consisting of parameters. The following parameter keys are available:

PARAMETERS

RETURNS

EXAMPLES

How to create a new render target and draw to it:

function init(self)
    -- render target buffer parameters
    local color_params = { format = render.FORMAT_RGBA,
                           width = render.get_window_width(),
                           height = render.get_window_height(),
                           min_filter = render.FILTER_LINEAR,
                           mag_filter = render.FILTER_LINEAR,
                           u_wrap = render.WRAP_CLAMP_TO_EDGE,
                           v_wrap = render.WRAP_CLAMP_TO_EDGE }
    local depth_params = { format = render.FORMAT_DEPTH,
                           width = render.get_window_width(),
                           height = render.get_window_height(),
                           u_wrap = render.WRAP_CLAMP_TO_EDGE,
                           v_wrap = render.WRAP_CLAMP_TO_EDGE }
    self.my_render_target = render.render_target("my_target", {[render.BUFFER_COLOR_BIT] = color_params, [render.BUFFER_DEPTH_BIT] = depth_params })
end

function update(self, dt)
    -- enable target so all drawing is done to it
    render.enable_render_target(self.my_render_target)

    -- draw a predicate to the render target
    render.draw(self.my_pred)
end

render.set_blend_func()

render.set_blend_func(source_factor,destination_factor)

Specifies the arithmetic used when computing pixel values that are written to the frame buffer. In RGBA mode, pixels can be drawn using a function that blends the source RGBA pixel values with the destination pixel values already in the frame buffer. Blending is initially disabled.

source_factor specifies which method is used to scale the source color components. destination_factor specifies which method is used to scale the destination color components.

Source color components are referred to as (R_s,G_s,B_s,A_s). Destination color components are referred to as (R_d,G_d,B_d,A_d). The color specified by setting the blendcolor is referred to as (R_c,G_c,B_c,A_c).

The source scale factor is referred to as (s_R,s_G,s_B,s_A). The destination scale factor is referred to as (d_R,d_G,d_B,d_A).

The color values have integer values between 0 and (k_R,k_G,k_B,k_A), where k_c = 2^m_c - 1 and m_c is the number of bitplanes for that color. I.e for 8 bit color depth, color values are between 0 and 255.

Available factor constants and corresponding scale factors:

The blended RGBA values of a pixel comes from the following equations:

• R_d = min(k_R, R_s * s_R + R_d * d_R)
• G_d = min(k_G, G_s * s_G + G_d * d_G)
• B_d = min(k_B, B_s * s_B + B_d * d_B)
• A_d = min(k_A, A_s * s_A + A_d * d_A)

Blend function (render.BLEND_SRC_ALPHA, render.BLEND_ONE_MINUS_SRC_ALPHA) is useful for drawing with transparency when the drawn objects are sorted from farthest to nearest. It is also useful for drawing antialiased points and lines in arbitrary order.

PARAMETERS

EXAMPLES

Set the blend func to the most common one:

render.set_blend_func(render.BLEND_SRC_ALPHA, render.BLEND_ONE_MINUS_SRC_ALPHA)

render.set_color_mask()

render.set_color_mask(red,green,blue,alpha)

Specifies whether the individual color components in the frame buffer is enabled for writing (true) or disabled (false). For example, if blue is false, nothing is written to the blue component of any pixel in any of the color buffers, regardless of the drawing operation attempted. Note that writing are either enabled or disabled for entire color components, not the individual bits of a component.

The component masks are all initially true.

PARAMETERS

EXAMPLES

-- alpha cannot be written to frame buffer
render.set_color_mask(true, true, true, false)

render.set_cull_face()

render.set_cull_face(face_type)

Specifies whether front- or back-facing polygons can be culled when polygon culling is enabled. Polygon culling is initially disabled.

If mode is render.FACE_FRONT_AND_BACK, no polygons are drawn, but other primitives such as points and lines are drawn. The initial value for face_type is render.FACE_BACK.

PARAMETERS

EXAMPLES

How to enable polygon culling and set front face culling:

render.enable_state(render.STATE_CULL_FACE)
render.set_cull_face(render.FACE_FRONT)

render.set_depth_func()

render.set_depth_func(func)

Specifies the function that should be used to compare each incoming pixel depth value with the value present in the depth buffer. The comparison is performed only if depth testing is enabled and specifies the conditions under which a pixel will be drawn.

Function constants:

• render.COMPARE_FUNC_NEVER (never passes)
• render.COMPARE_FUNC_LESS (passes if the incoming depth value is less than the stored value)
• render.COMPARE_FUNC_LEQUAL (passes if the incoming depth value is less than or equal to the stored value)
• render.COMPARE_FUNC_GREATER (passes if the incoming depth value is greater than the stored value)
• render.COMPARE_FUNC_GEQUAL (passes if the incoming depth value is greater than or equal to the stored value)
• render.COMPARE_FUNC_EQUAL (passes if the incoming depth value is equal to the stored value)
• render.COMPARE_FUNC_NOTEQUAL (passes if the incoming depth value is not equal to the stored value)
• render.COMPARE_FUNC_ALWAYS (always passes)

The depth function is initially set to render.COMPARE_FUNC_LESS.

PARAMETERS

EXAMPLES

Enable depth test and set the depth test function to "not equal".

render.enable_state(render.STATE_DEPTH_TEST)
render.set_depth_func(render.COMPARE_FUNC_NOTEQUAL)

render.set_depth_mask()

render.set_depth_mask(depth)

Specifies whether the depth buffer is enabled for writing. The supplied mask governs if depth buffer writing is enabled (true) or disabled (false).

The mask is initially true.

PARAMETERS

EXAMPLES

How to turn off writing to the depth buffer:

render.set_depth_mask(false)

render.set_polygon_offset()

render.set_polygon_offset(factor,units)

Sets the scale and units used to calculate depth values. If render.STATE_POLYGON_OFFSET_FILL is enabled, each fragment's depth value is offset from its interpolated value (depending on the depth value of the appropriate vertices). Polygon offset can be used when drawing decals, rendering hidden-line images etc.

factor specifies a scale factor that is used to create a variable depth offset for each polygon. The initial value is 0.

units is multiplied by an implementation-specific value to create a constant depth offset. The initial value is 0.

The value of the offset is computed as factor × DZ + r × units

DZ is a measurement of the depth slope of the polygon which is the change in z (depth) values divided by the change in either x or y coordinates, as you traverse a polygon. The depth values are in window coordinates, clamped to the range [0, 1].

r is the smallest value that is guaranteed to produce a resolvable difference. It's value is an implementation-specific constant.

The offset is added before the depth test is performed and before the value is written into the depth buffer.

PARAMETERS

EXAMPLES

render.enable_state(render.STATE_POLYGON_OFFSET_FILL)
render.set_polygon_offset(1.0, 1.0)

render.set_projection()

render.set_projection(matrix)

Sets the projection matrix to use when rendering.

PARAMETERS

EXAMPLES

How to set the projection to orthographic with world origo at lower left, width and height as set in project settings and depth (z) between -1 and 1:

render.set_projection(vmath.matrix4_orthographic(0, render.get_width(), 0, render.get_height(), -1, 1))

render.set_render_target()

render.set_render_target(render_target,[options])

Sets a render target. Subsequent draw operations will be to the render target until it is replaced by a subsequent call to set_render_target.

PARAMETERS

EXAMPLES

How to set a render target and draw to it and then switch back to the default render target The render target defines the depth/stencil buffers as transient, when set_render_target is called the next time the buffers may be invalidated and allow for optimisations depending on driver support

function update(self, dt)
    -- set render target so all drawing is done to it
    render.set_render_target(self.my_render_target, { transient = { render.BUFFER_DEPTH_BIT, render.BUFFER_STENCIL_BIT } } )

    -- draw a predicate to the render target
    render.draw(self.my_pred)

    -- set default render target. This also invalidates the depth and stencil buffers of the current target (self.my_render_target)
    --  which can be an optimisation on some hardware
    render.set_render_target(render.RENDER_TARGET_DEFAULT)

end

render.set_render_target_size()

render.set_render_target_size(render_target,width,height)

PARAMETERS

EXAMPLES

Set the render target size to the window size:

render.set_render_target_size(self.my_render_target, render.get_window_width(), render.get_window_height())

render.set_stencil_func()

render.set_stencil_func(func,ref,mask)

Stenciling is similar to depth-buffering as it enables and disables drawing on a per-pixel basis. First, GL drawing primitives are drawn into the stencil planes. Second, geometry and images are rendered but using the stencil planes to mask out where to draw.

The stencil test discards a pixel based on the outcome of a comparison between the reference value ref and the corresponding value in the stencil buffer.

func specifies the comparison function. See the table below for values. The initial value is render.COMPARE_FUNC_ALWAYS.

ref specifies the reference value for the stencil test. The value is clamped to the range [0, 2ⁿ-1], where n is the number of bitplanes in the stencil buffer. The initial value is 0.

mask is ANDed with both the reference value and the stored stencil value when the test is done. The initial value is all 1's.

Function constant:

• render.COMPARE_FUNC_NEVER (never passes)
• render.COMPARE_FUNC_LESS (passes if (ref & mask) < (stencil & mask))
• render.COMPARE_FUNC_LEQUAL (passes if (ref & mask) <= (stencil & mask))
• render.COMPARE_FUNC_GREATER (passes if (ref & mask) > (stencil & mask))
• render.COMPARE_FUNC_GEQUAL (passes if (ref & mask) >= (stencil & mask))
• render.COMPARE_FUNC_EQUAL (passes if (ref & mask) = (stencil & mask))
• render.COMPARE_FUNC_NOTEQUAL (passes if (ref & mask) != (stencil & mask))
• render.COMPARE_FUNC_ALWAYS (always passes)

PARAMETERS

EXAMPLES

-- let only 0's pass the stencil test
render.set_stencil_func(render.COMPARE_FUNC_EQUAL, 0, 1)

render.set_stencil_mask()

render.set_stencil_mask(mask)

The stencil mask controls the writing of individual bits in the stencil buffer. The least significant n bits of the parameter mask, where n is the number of bits in the stencil buffer, specify the mask.

Where a 1 bit appears in the mask, the corresponding bit in the stencil buffer can be written. Where a 0 bit appears in the mask, the corresponding bit in the stencil buffer is never written.

The mask is initially all 1's.

PARAMETERS

EXAMPLES

-- set the stencil mask to all 1:s
render.set_stencil_mask(0xff)

render.set_stencil_op()

render.set_stencil_op(sfail,dpfail,dppass)

The stencil test discards a pixel based on the outcome of a comparison between the reference value ref and the corresponding value in the stencil buffer. To control the test, call render.set_stencil_func.

This function takes three arguments that control what happens to the stored stencil value while stenciling is enabled. If the stencil test fails, no change is made to the pixel's color or depth buffers, and sfail specifies what happens to the stencil buffer contents.

Operator constants:

• render.STENCIL_OP_KEEP (keeps the current value)
• render.STENCIL_OP_ZERO (sets the stencil buffer value to 0)
• render.STENCIL_OP_REPLACE (sets the stencil buffer value to ref, as specified by render.set_stencil_func)
• render.STENCIL_OP_INCR (increments the stencil buffer value and clamp to the maximum representable unsigned value)
• render.STENCIL_OP_INCR_WRAP (increments the stencil buffer value and wrap to zero when incrementing the maximum representable unsigned value)
• render.STENCIL_OP_DECR (decrements the current stencil buffer value and clamp to 0)
• render.STENCIL_OP_DECR_WRAP (decrements the current stencil buffer value and wrap to the maximum representable unsigned value when decrementing zero)
• render.STENCIL_OP_INVERT (bitwise inverts the current stencil buffer value)

dppass and dpfail specify the stencil buffer actions depending on whether subsequent depth buffer tests succeed (dppass) or fail (dpfail).

The initial value for all operators is render.STENCIL_OP_KEEP.

PARAMETERS

EXAMPLES

Set the stencil function to never pass and operator to always draw 1's on test fail.

render.set_stencil_func(render.COMPARE_FUNC_NEVER, 1, 0xFF)
-- always draw 1's on test fail
render.set_stencil_op(render.STENCIL_OP_REPLACE, render.STENCIL_OP_KEEP, render.STENCIL_OP_KEEP)

render.set_view()

render.set_view(matrix)

Sets the view matrix to use when rendering.

PARAMETERS

EXAMPLES

How to set the view and projection matrices according to the values supplied by a camera.

function init(self)
  self.view = vmath.matrix4()
  self.projection = vmath.matrix4()
end

function update(self, dt)
  -- set the view to the stored view value
  render.set_view(self.view)
  -- now we can draw with this view
end

function on_message(self, message_id, message)
  if message_id == hash("set_view_projection") then
     -- camera view and projection arrives here.
     self.view = message.view
     self.projection = message.projection
  end
end

render.set_viewport()

render.set_viewport(x,y,width,height)

Set the render viewport to the specified rectangle.

PARAMETERS

EXAMPLES

-- Set the viewport to the window dimensions.
render.set_viewport(0, 0, render.get_window_width(), render.get_window_height())

Constants

render.BLEND_CONSTANT_ALPHA

render.BLEND_CONSTANT_COLOR

render.BLEND_DST_ALPHA

render.BLEND_DST_COLOR

render.BLEND_ONE

render.BLEND_ONE_MINUS_CONSTANT_ALPHA

render.BLEND_ONE_MINUS_CONSTANT_COLOR

render.BLEND_ONE_MINUS_DST_ALPHA

render.BLEND_ONE_MINUS_DST_COLOR

render.BLEND_ONE_MINUS_SRC_ALPHA

render.BLEND_ONE_MINUS_SRC_COLOR

render.BLEND_SRC_ALPHA

render.BLEND_SRC_ALPHA_SATURATE

render.BLEND_SRC_COLOR

render.BLEND_ZERO

render.BUFFER_COLOR_BIT

render.BUFFER_DEPTH_BIT

render.BUFFER_STENCIL_BIT

render.COMPARE_FUNC_ALWAYS

render.COMPARE_FUNC_EQUAL

render.COMPARE_FUNC_GEQUAL

render.COMPARE_FUNC_GREATER

render.COMPARE_FUNC_LEQUAL

render.COMPARE_FUNC_LESS

render.COMPARE_FUNC_NEVER

render.COMPARE_FUNC_NOTEQUAL

render.FACE_BACK

render.FACE_FRONT

render.FACE_FRONT_AND_BACK

render.FILTER_LINEAR

render.FILTER_NEAREST

render.FORMAT_DEPTH

render.FORMAT_LUMINANCE

render.FORMAT_RGB

render.FORMAT_RGBA

render.FORMAT_RGBA_DXT1

render.FORMAT_RGBA_DXT3

render.FORMAT_RGBA_DXT5

render.FORMAT_RGB_DXT1

render.FORMAT_STENCIL

render.RENDER_TARGET_DEFAULT

render.STATE_BLEND

render.STATE_CULL_FACE

render.STATE_DEPTH_TEST

render.STATE_POLYGON_OFFSET_FILL

render.STATE_STENCIL_TEST

render.STENCIL_OP_DECR

render.STENCIL_OP_DECR_WRAP

render.STENCIL_OP_INCR

render.STENCIL_OP_INCR_WRAP

render.STENCIL_OP_INVERT

render.STENCIL_OP_KEEP

render.STENCIL_OP_REPLACE

render.STENCIL_OP_ZERO

render.WRAP_CLAMP_TO_BORDER

render.WRAP_CLAMP_TO_EDGE

render.WRAP_MIRRORED_REPEAT

render.WRAP_REPEAT

Messages

clear_color

set clear color

Set render clear color. This is the color that appears on the screen where nothing is rendered, i.e. background.

EXAMPLES

msg.post("@render:", "clear_color", { color = vmath.vector4(1, 0, 0, 0) } )

draw_debug_text

draw a text on the screen

Draw a text on the screen. This should be used for debugging purposes only.

EXAMPLES

msg.post("@render:", "draw_debug_text", { text = "Hello world!", position = vmath.vector3(200, 200, 0), color = vmath.vector4(1, 0, 0, 1) } )

draw_line

draw a line on the screen

Draw a line on the screen. This should mostly be used for debugging purposes.

EXAMPLES

-- draw a white line from (200, 200) to (200, 300)
msg.post("@render:", "draw_line", { start_point = vmath.vector3(200, 200, 0), end_point = vmath.vector3(200, 300, 0), color = vmath.vector4(1, 1, 1, 1) } )

resize

resizes the window

Set the size of the game window. Only works on desktop platforms.

EXAMPLES

msg.post("@render:", "resize", { width = 1024, height = 768 } )

window_resized

reports a window size change

Reports a change in window size. This is initiated on window resize on desktop or by orientation changes on mobile devices.

EXAMPLES

function on_message(self, message_id, message)
    -- check for the message
    if message_id == hash("window_resized") then
        -- the window was resized.
    end
end