画布项目着色器(CanvasItem shaders)：Godot的2D着色器

译者注:直译为***画布项目着色器***下文中将意译成2D着色器画布项目着色器(CanvasItem shaders)2D着色器用于绘制Godot中的所有的2D元素包括所有继承于CanvasItem的节点以及所有的GUI元素。相对于3D着色器2D着色器要简单一些内置函数也比较少但是2D和3D着色器的基础结构是相同的都包顶点函数(vertex)片元函数(fragment)及光(light)函数渲染模式画布元素渲染模式描述blend_mixMix blend mode (alpha is transparency), default.blend_addAdditive blend mode.blend_subSubtractive blend mode.blend_mulMultiplicative blend mode.blend_premul_alphaPre-multiplied alpha blend mode.blend_disabledDisable blending, values (including alpha) are written as-is.unshadedResult is just albedo. No lighting/shading happens in material.light_onlyOnly draw on light pass.skip_vertex_transformVERTEX/NORMAL/etc need to be transformed manually in vertex function.译者注:vertex built-in,fragment built-in 以及 light built-in根据其实际作用分别被意译为内置顶点属性内置片元属性以及内置光属性属性一词借用C#中的属性即property,其实就是getter和setter内置顶点属性(vertex built-ins)当值注明为in时意味着只读当值注明为out时意味着可以选择性地写入但是并不一定提供一个有效值。当值注明为inout时它会提供一个有效的默认值并且可以选择性地写入。采样器(sampler)不是可写对象它们也没有被标记。顶点数据(VERTEX)使用局部坐标表示(相对于摄像机的像素坐标)如果不改写的话它们的值会原封不动地传递出去。用户可以关闭内置***模型视图变换***(英文:modelview transform,注:但投影(projection)依然会发生)并使用如下代码手动实现:shader_type canvas_item; render_mode skip_vertex_transform; ​ void vertex() { ​ VERTEX (EXTRA_MATRIX * (WORLD_MATRIX * vec4(VERTEX, 0.0, 1.0))).xy; }注意WORLD_MATRIX实际上是一个模型视图矩阵它接受局部坐标的输入然后将其变换到视图空间。如果想要获取一个顶点的世界坐标你必须按照如下方法传入一个自定义的uniform值:material.set_shader_param(global_transform, get_global_transform())然后在你的顶点着色器部分:uniform mat4 global_transform; varying vec2 world_position; ​ void vertex(){ world_position (global_transform * vec4(VERTEX, 0.0, 1.0)).xy; }然后在顶点和片元函数中就都可以使用world_position了。诸如UV和COLOR等一些内置成员如果不加修改的话也会被传入片元函数。例如INSTANCE_CUSTOM变量包含着实例的自定义数据。在粒子中这些数据往往如下所示:x: Rotation angle in radians.y: Phase during lifetime (0 to 1).z: Animation frame.内置顶点属性描述in mat4 WORLD_MATRIX图片空间(Image space)到视图空间(view space)的变换in mat4 EXTRA_MATRIXExtra transform.in mat4 PROJECTION_MATRIXView space to clip space transform.in float TIMEGlobal time, in seconds.in vec4 INSTANCE_CUSTOMInstance custom data.in bool AT_LIGHT_PASSTrue if this is a light pass.inout vec2 VERTEXVertex, in image space.in vec2 TEXTURE_PIXEL_SIZENormalized pixel size of default 2D texture. For a Sprite with a texture of size 64x32px, TEXTURE_PIXEL_SIZE vec2(1/64, 1/32)inout vec2 UVUV.inout vec4 COLORColor from vertex primitive.inout float POINT_SIZEPoint size for point drawing.内置片元属性(Fragment built-ins)一些节点(例如:Sprite)会显示一个默认的纹理。然而当给这些节点添加了自定义片元函数以后纹理的查找则需要手动来完成。在内置属性COLOR中Godot并没有提供纹理的颜色。如果想在这些节点中读取纹理颜色需要如下方法:COLOR texture(TEXTURE, UV);这和法线贴图有所不同如果一个节点添加了法线贴图则Godot可以默认使用它并且把它赋值给内置的NORMAL属性。如果你使用了一个本用于3D的法线贴图它将呈现为翻转状态。如果你想在自己的Shader中使用它你需要把它赋值给NORMALMAP属性Godot会把它转换成2D模式并重写NORMAL属性NORMALMAP texture(NORMAL_TEXTURE, UV).rgb;内置片元属性描述in vec4FRAGCOORDFragment coordinate, pixel adjusted.inout vec3NORMALNormal read fromNORMAL_TEXTURE. Writable.out vec3NORMALMAPConfigures normal maps meant for 3D for use in 2D. If used, overwritesNORMAL.inout floatNORMALMAP_DEPTHNormalmap depth for scaling.in vec2UVUV from vertex function.inout vec4COLORColor from vertex function and output fragment color. If unused, will be set toTEXTUREcolor.in sampler2DTEXTUREDefault 2D texture.in sampler2DNORMAL_TEXTUREDefault 2D normal texture.in vec2TEXTURE_PIXEL_SIZENormalized pixel size of default 2D texture. For a Sprite with a texture of size 64x32px,TEXTURE_PIXEL_SIZEvec2(1/64, 1/32)in vec2SCREEN_UVScreen UV for use withSCREEN_TEXTURE.in vec2SCREEN_PIXEL_SIZESize of individual pixels. Equal to inverse of resolution.in vec2POINT_COORDCoordinate for drawing points.in floatTIMEGlobal time in seconds.in boolAT_LIGHT_PASSTrue if this is a light pass.in sampler2DSCREEN_TEXTUREScreen texture, mipmaps contain gaussian blurred versions.内置光属性(Light built-ins)相对于3D着色器2D着色器光函数的工作方式有所不同。在2D着色器中光函数会在物体被绘制的时候调用一次然后对场景中每一个触及到这个物体的光都调用一次。如果你不希望任何光影响到某一个物体可以使用unshaded渲染模式。如果你只希望一个物体被光覆盖的地方可见那么可以使用light_only渲染模式。当一个着色器(所属的物体)处于光照中时内置光属性AT_LIGHT_PASS的值将为true内置光属性描述in vec4FRAGCOORDFragment coordinate of pixel center. Origin at lower left.in vec3NORMALInput Normal. Although this value is passed in,normal calculation still happens outside of this function.in vec2UVUV from vertex function, equivalent to the UV in the fragment function.in vec4COLORInput Color. This is the output of the fragment function with final modulation applied.sampler2DTEXTURECurrent texture in use for CanvasItem.in vec2TEXTURE_PIXEL_SIZENormalized pixel size of default 2D texture. For a Sprite with a texture of size 64x32px,TEXTURE_PIXEL_SIZEvec2(1/64, 1/32)in vec2SCREEN_UVSCREEN_TEXTURECoordinate (for using with screen texture).in vec2POINT_COORDUV for Point Sprite.in floatTIMEGlobal time in seconds.inout vec2LIGHT_VECVector from light to fragment, can be modified to alter shadow computation.inout floatLIGHT_HEIGHTHeight of Light. Only effective when normals are used.inout vec4LIGHT_COLORColor of Light.in vec2LIGHT_UVUV for Light texture.out vec4SHADOW_COLORShadow Color of Light.inout vec4LIGHTValue from the Light texture and output color. Can be modified. If not used, the light function is ignored.