love.graphics.newShader

Available since LÖVE 0.9.0
It has been renamed from love.graphics.newPixelEffect.


O.png This function can be slow if it is called repeatedly, such as from love.update or love.draw. If you need to use a specific resource often, create it once and store it somewhere it can be reused!  



Creates a new Shader object for hardware-accelerated vertex and pixel effects. A Shader contains either vertex shader code, pixel shader code, or both.

Shaders are small programs which are run on the video card when drawing. Vertex shaders are run once for each vertex (for example, an image has 4 vertices - one at each corner. A Mesh might have many more.) Pixel shaders are run once for each pixel on the screen which the drawn object touches. Pixel shader code is executed after all the object's vertices have been processed by the vertex shader.

Function

Synopsis

shader = love.graphics.newShader( code )

Arguments

string code
The pixel shader or vertex shader code, or a filename pointing to a file with the code.

Returns

Shader shader
A Shader object for use in drawing operations.

Function

Synopsis

shader = love.graphics.newShader( pixelcode, vertexcode )

Arguments

string pixelcode
The pixel shader code, or a filename pointing to a file with the code.
string vertexcode
The vertex shader code, or a filename pointing to a file with the code.

Returns

Shader shader
A Shader object for use in drawing operations.

Notes

The pixelcode and vertexcode arguments can be in any order.

Shader Language

Shaders are not programmed in Lua, but by using a special shader language instead. The shader language is basically GLSL 1.20 (specs) with a few aliases added for existing types:

GLSL LÖVE shader language
float number
sampler2D Image
uniform extern
texture2D(tex, uv) Texel(tex, uv)

Vertex shader code must contain at least one function, named position, which is the function that will produce transformed vertex positions of drawn objects in screen-space.

Pixel shader code must contain at least one function, named effect, which is the function that will produce the color which is blended onto the screen for each pixel a drawn object touches.

Additionally, LÖVE exposes a function VideoTexel(uv) which yields the color value of the currently drawn video at that position. Since Videos are drawn as YUV data, in multiple textures, and then converted in the shader, the Texel function cannot be used.

Pixel Shader Function

When an object is drawn, the pixel shader effect function is called hundreds or thousands of times: once for each pixel on the screen that the object touches. The pixel shader is run after the vertex shader, if there is one.

Synopsis

vec4 effect( vec4 color, Image texture, vec2 texture_coords, vec2 screen_coords )

Arguments

vec4 color
The drawing color set with love.graphics.setColor or the per-vertex Mesh color.
Image texture
The texture of the image or canvas being drawn.
vec2 texture_coords
The location inside the texture to get pixel data from. Texture coordinates are usually normalized to the range of (0, 0) to (1, 1), with the top-left corner being (0, 0).
vec2 screen_coords
Coordinates of the pixel on the screen. Pixel coordinates are not normalized (unlike texture coordinates). (0.5, 0.5) represents the top left of the screen (bottom left in LÖVE versions prior to 0.10.0).

Returns

vec4 output_color
The color of the pixel.

Notes

If no pixel shader is used, LÖVE internally uses a default. This is its code: 

vec4 effect(vec4 color, Image texture, vec2 texture_coords, vec2 screen_coords)
{
    vec4 texturecolor = Texel(texture, texture_coords);
    return texturecolor * color;
}

Or for Video 

vec4 effect(vec4 color, Image texture, vec2 texture_coords, vec2 screen_coords)
{
    vec4 texturecolor = VideoTexel(texture_coords);
    return texturecolor * color;
}

If multiple canvases are being rendered to simultaneously (by giving multiple Canvas parameters to love.graphics.setCanvas), you can use the void effect (no arguments!) function instead of vec4 effect in order to output a separate color to each Canvas. It has the following prototype: 

void effect()
{
    // love_Canvases is a writable array of vec4 colors. Each index corresponds to a Canvas.
    // IMPORTANT: If you don't assign a value to all active canvases, bad things will happen.
    love_Canvases[0] = color;
    love_Canvases[1] = color + vec4(0.5);
    // etc.
}

If you wish to get the arguments that are passed to the single-canvas version (vec4 effect), see the built-in Shader Variables. color will be in VaryingColor, texture_coords will be in VaryingTexCoord and screen_coords is in love_PixelCoord. And if you wish to access the texture used in the drawing operation, you can do that by defining a uniform texture (of the appropriate type) named MainTex or by sending it yourself via Shader:send.

Vertex Shader Function

Synopsis

vec4 position( mat4 transform_projection, vec4 vertex_position )

Arguments

mat4 transform_projection
The transformation matrix affected by love.graphics.translate and friends combined with the orthographic projection matrix.
vec4 vertex_position
The raw un-transformed position of the current vertex.

Returns

vec4 output_pos
The final transformed position of the current vertex.

Notes

If no vertex shader code is used, LÖVE uses a default. This is its code: 

vec4 position(mat4 transform_projection, vec4 vertex_position)
{
    // The order of operations matters when doing matrix multiplication.
    return transform_projection * vertex_position;
}

Notes

Vertex shader code is run for every vertex drawn to the screen (for example, love.graphics.rectangle will produce 4 vertices) and is used to transform the vertex positions from their original coordinates into screen-space, as well as to send information such as per-vertex color and texture coordinate values to the pixel shader.

Pixel shader code is run for every pixel on the screen that a drawn object touches, and is used to produce the color that will be blended onto the screen at that pixel, often by reading from an image. Pixel shaders are sometimes called fragment shaders.

The varying keyword can be used to set a value in the vertex shader and have it interpolated in between vertices and passed down to the pixel shader.

Vertex and Pixel shader code can be combined into one file or string if you wrap the vertex-specific code in #ifdef VERTEX .. #endif and the pixel-specific code in #ifdef PIXEL .. #endif.

Built-in variables

LÖVE provides several built-in variables for both pixel and vertex shaders. The full list can be found here: Shader Variables.

Examples

Create a shader using vertex and pixel shader code which behaves as if no shader is set.

local pixelcode = [[
    vec4 effect( vec4 color, Image texture, vec2 texture_coords, vec2 screen_coords )
    {
        vec4 texcolor = Texel(texture, texture_coords);
        return texcolor * color;
    }
]]

local vertexcode = [[
    vec4 position( mat4 transform_projection, vec4 vertex_position )
    {
        return transform_projection * vertex_position;
    }
]]

shader = love.graphics.newShader(pixelcode, vertexcode)

function love.draw()
    love.graphics.setShader(shader)
    -- draw things
    love.graphics.setShader()
    -- draw more things
end

Access the pre-transformed vertex position in the pixel shader with the varying keyword.

vertex shader code

varying vec4 vpos;

vec4 position( mat4 transform_projection, vec4 vertex_position )
{
    vpos = vertex_position;
    return transform_projection * vertex_position;
}

pixel shader code

varying vec4 vpos;

vec4 effect( vec4 color, Image texture, vec2 texture_coords, vec2 screen_coords )
{
    texture_coords += vec2(cos(vpos.x), sin(vpos.y));
    vec4 texcolor = Texel(texture, texture_coords);
    return texcolor * color;
}

Combine the above example into one string or file with the help of #ifdef.

varying vec4 vpos;

#ifdef VERTEX
vec4 position( mat4 transform_projection, vec4 vertex_position )
{
    vpos = vertex_position;
    return transform_projection * vertex_position;
}
#endif

#ifdef PIXEL
vec4 effect( vec4 color, Image texture, vec2 texture_coords, vec2 screen_coords )
{
    texture_coords += vec2(cos(vpos.x), sin(vpos.y));
    vec4 texcolor = Texel(texture, texture_coords);
    return texcolor * color;
}
#endif

See Also


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