笔者介绍：姜雪伟，IT公司技术合伙人，IT高级讲师，CSDN社区专家，特邀编辑，畅销书作者，已出版书籍：《手把手教你架构3D游戏引擎》电子工业出版社和《Unity3D实战核心技术详解》电子工业出版社等。
CSDN视频网址：http://edu.csdn.net/lecturer/144
当前市面上比较流行的引擎无非是Unity3D引擎和UE4虚幻4，但是作为开源的Ogre引擎还是被一部分玩家所喜欢，由于其开源的，而且是针对图形处理的。所以对于学习3D游戏开发者来说，学习Ogre的GPU渲染是一条捷径，各个引擎的渲染Shader编写其实是类似的，它们的区别是在细节方面，虚幻做的最好，其他就是Unity和Ogre了。下面把Ogre的处理方式给读者介绍一下：
高光，法线，环境映射对于Shader来说必须要掌握的，其中Ogre中的渲染需要几个文件一是cg文件还有material文件，先给读者展示cg文件，代码如下所示：
struct VIn
{
float4 p : POSITION;
float3 n : NORMAL;
float3 t : TANGENT;
float2 uv : TEXCOORD0;
};
struct VOut
{
float4 p : POSITION;
float2 uv : TEXCOORD0;
float4 wp : TEXCOORD1;
float3 n : TEXCOORD2;
float3 t : TEXCOORD3;
float3 b : TEXCOORD4;
float4 lp : TEXCOORD5;
float3 sdir : TEXCOORD6;
};
struct PIn
{
float2 uv : TEXCOORD0;
float4 wp : TEXCOORD1;
float3 n : TEXCOORD2;
float3 t : TEXCOORD3;
float3 b : TEXCOORD4;
float4 lp : TEXCOORD5;
float3 sdir : TEXCOORD6;
};
void ambient_vs(VIn IN,
uniform float4x4 wvpMat,
out float4 oPos : POSITION,
out float2 oUV : TEXCOORD0)
{
oPos = mul(wvpMat, IN.p);
oUV = IN.uv;
}
float4 ambient_ps(in float2 uv : TEXCOORD0,
uniform float3 ambient,
uniform float4 matDif,
uniform sampler2D dMap,
uniform sampler2D aoMap): COLOR0
{
return tex2D(dMap, uv) * tex2D(aoMap, uv) *
float4(ambient, 1) * float4(matDif.rgb, 1);
}
VOut diffuse_vs(VIn IN,
uniform float4x4 wMat,
uniform float4x4 wvpMat,
uniform float4x4 tvpMat,
uniform float4 spotlightDir)
{
VOut OUT;
OUT.wp = mul(wMat, IN.p);
OUT.p = mul(wvpMat, IN.p);
OUT.uv = IN.uv;
OUT.n = IN.n;
OUT.t = IN.t;
OUT.b = cross(IN.t, IN.n);
OUT.sdir = mul(wMat, spotlightDir).xyz; // spotlight dir in world space
OUT.lp = mul(tvpMat, OUT.wp);
return OUT;
}
float4 diffuse_ps(
PIn IN,
uniform float3 lightDif0,
uniform float4 lightPos0,
uniform float4 lightAtt0,
uniform float3 lightSpec0,
uniform float4 matDif,
uniform float4 matSpec,
uniform float matShininess,
uniform float3 camPos,
uniform float4 invSMSize,
uniform float4 spotlightParams,
uniform float4x4 iTWMat,
uniform sampler2D diffuseMap : TEXUNIT0,
uniform sampler2D specMap : TEXUNIT1,
uniform sampler2D normalMap : TEXUNIT2): COLOR0
{
// direction
float3 ld0 = normalize(lightPos0.xyz - (lightPos0.w * IN.wp.xyz));
half lightDist = length(lightPos0.xyz - IN.wp.xyz) / lightAtt0.r;
// attenuation
half ila = lightDist * lightDist; // quadratic falloff
half la = 1.0 - ila;
float4 normalTex = tex2D(normalMap, IN.uv);
float3x3 tbn = float3x3(IN.t, IN.b, IN.n);
float3 normal = mul(transpose(tbn), normalTex.xyz * 2 - 1); // to object space
normal = normalize(mul((float3x3)iTWMat, normal));
float3 diffuse = max(dot(ld0, normal), 0);
// calculate the spotlight effect
float spot = (spotlightParams.x == 1 &&
spotlightParams.y == 0 &&
spotlightParams.z == 0 &&
spotlightParams.w == 1 ? 1 : // if so, then it's not a spot light
saturate(
(dot(ld0, normalize(-IN.sdir)) - spotlightParams.y) /
(spotlightParams.x - spotlightParams.y)));
float3 camDir = normalize(camPos - IN.wp.xyz);
float3 halfVec = normalize(ld0 + camDir);
float3 specular = pow(max(dot(normal, halfVec), 0), matShininess);
float4 diffuseTex = tex2D(diffuseMap, IN.uv);
float4 specTex = tex2D(specMap, IN.uv);
float3 diffuseContrib = (diffuse * lightDif0 * diffuseTex.rgb * matDif.rgb);
float3 specularContrib = (specular * lightSpec0 * specTex.rgb * matSpec.rgb);
float3 light0C = (diffuseContrib + specularContrib) * la * spot;
return float4(light0C, diffuseTex.a);
}其中VIn表示的是顶点输入的结构体，VOut表示的是顶点输出的结构体，PIn表示的是片段着色器的输入结构体，在下面的函数实现中首先实现的是ambient occlusion mapping也包括顶点和片段处理。最后是diffuse的顶点和片段处理也就是高光specluar和法线normal的处理，这样整个Shader就完成了。
下面实现的是material的编写，代码如下所示：
material base_material
{
set $diffuseCol "1 1 1 1"
set $specularCol "1 1 1"
set $shininess "32"
technique
{
pass
{
illumination_stage ambient
ambient 1 1 1 1
diffuse $diffuseCol
specular 0 0 0 0
emissive 0 0 0 0
vertex_program_ref ambient_vs
{
}
fragment_program_ref ambient_ps
{
}
texture_unit diffuseMap
{
texture white.png
}
texture_unit aoMap
{
texture white.png
}
}
pass
{
illumination_stage per_light
scene_blend add
// iteration once_per_light not needed while illumination_stage per_light is used
vertex_program_ref diffuse_vs
{
}
fragment_program_ref diffuse_ps
{
}
diffuse $diffuseCol
specular $specularCol $shininess
ambient 0 0 0 0
texture_unit diffuseMap
{
texture white.png
}
texture_unit specMap
{
texture white.png
}
texture_unit normalMap
{
texture flat_n.png
}
}
}
}
// examples (require the appropriate [[textures]], all found in the Ogre samples)
material rockwall : base_material
{
set_texture_alias diffuseMap rockwall.tga
set_texture_alias specMap rockwall.tga
set_texture_alias normalMap rockwall_NH.tga
}
material metal : base_material
{
set_texture_alias diffuseMap RustedMetal.jpg
set_texture_alias specMap RustedMetal.jpg
}
material ogre : base_material
{
set_texture_alias diffuseMap GreenSkin.jpg
set_texture_alias specMap GreenSkin.jpg
set_texture_alias normalMap NMHollyBumps.png
}该文件实现了一个基材质 base_material其它材质可以继承，这个对于开发者来说非常灵活。另外还需要一个program程序文件用于shader和图片的配置，代码如下所示：
vertex_program diffuse_vs cg
{
source general.cg
profiles vs_1_1 arbvp1
entry_point diffuse_vs
default_params
{
param_named_auto wMat world_matrix
param_named_auto wvpMat worldviewproj_matrix
param_named_auto tvpMat texture_viewproj_matrix 0
param_named_auto spotlightDir light_direction_object_space 0
}
}
vertex_program ambient_vs cg
{
source general.cg
profiles vs_1_1 arbvp1
entry_point ambient_vs
default_params
{
param_named_auto wvpMat worldviewproj_matrix
}
}
fragment_program ambient_ps cg
{
source general.cg
profiles ps_2_0 arbfp1
entry_point ambient_ps
default_params
{
param_named_auto ambient ambient_light_colour
param_named_auto matDif surface_diffuse_colour
}
}
fragment_program diffuse_ps cg
{
source general.cg
profiles ps_2_x arbfp1
entry_point diffuse_ps
default_params
{
param_named_auto lightDif0 light_diffuse_colour 0
param_named_auto lightSpec0 light_specular_colour 0
param_named_auto camPos camera_position
param_named_auto matShininess surface_shininess
param_named_auto matDif surface_diffuse_colour
param_named_auto matSpec surface_specular_colour
param_named_auto lightPos0 light_position 0
param_named_auto lightAtt0 light_attenuation 0
param_named_auto iTWMat inverse_transpose_world_matrix
param_named_auto spotlightParams spotlight_params 0
}
}以上就完成了高光，法线以及ambient Shader的实现，当然学习Shader编程不能仅限于功能实现，还需要举一反三，比如我们上面封装的base_material。还是可以继续去扩展的，代码如下所示：
material some_material : base_material
{
// any of these maps can be left out if you don't have one
set_texture_alias diffuseMap some_dif.png
set_texture_alias specMap some_spec.png
set_texture_alias normalMap some_norm.png
set_texture_alias aoMap some_ao.png
// diffuse colour multiplier (for example, green-ish)
set $diffuseCol "0.1 1 0.1"
// specular colour multiplier (for example, red-ish)
set $specularCol "1 0.1 0.1"
// specular power (shininess) (the higher, the sharper the highlights)
set $shininess "128"
// once again, you can leave any of these configurables out if you don't need them
}我们还可以在此Shader的基础上实现UV镜像处理，修改代码如下所示：
一、首先将VIn输入结构体修改如下所示：
struct VIn
{
float4 p : POSITION;
float3 n : NORMAL;
float4 t : TANGENT; // <- this was changed
float2 uv : TEXCOORD0;
};二、修改Vout输出结构体代码如下：
struct VOut
{
float4 p : POSITION;
float2 uv : TEXCOORD0;
float4 wp : TEXCOORD1;
float3 n : TEXCOORD2;
float4 t : TEXCOORD3; //<- this was changed
float3 b : TEXCOORD4;
float4 lp : TEXCOORD5;
float3 sdir : TEXCOORD6;
};三、修改diffuse_vs函数代码修改如下所示：
VOut diffuse_vs(VIn IN,
uniform float4x4 wMat,
uniform float4x4 wvpMat,
uniform float4x4 tvpMat,
uniform float4 spotlightDir)
{
VOut OUT;
OUT.wp = mul(wMat, IN.p);
OUT.p = mul(wvpMat, IN.p);
OUT.uv = IN.uv;
OUT.n = IN.n;
OUT.t = IN.t;
OUT.b = cross(IN.t.xyz, IN.n) * IN.t.w; //<-this was changed
OUT.sdir = mul(wMat, spotlightDir).xyz; // spotlight dir in world space
OUT.lp = mul(tvpMat, OUT.wp);
return OUT;
}关于变动的代码都加了注释，对比源代码既可以看明白，到此结束。。。。。。。
作者：jxw167 发表于2017/6/1 11:32:15 原文链接
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