OpenGL深入探索——OpenGL/GLSL数据传递小记(3.x) 【包含UBO详解】
【摘要】
OpenGL/GLSL规范在不断演进着，我们渐渐走进可编程管道的时代的同时，崭新的功能接口也让我们有点缭乱的感觉。本文再次从OpenGL和GLSL之间数据的传递这一点，记录和介绍基于OpenGL3.x的新方式，也会适时介绍Unform Buffer Objecct(UBO)这一重要特性。——ZwqXin.com
本文可视为大致一...
1. attribute变量
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glsl3.x代码 (Vertex Program)
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#version 330
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layout(location = 0) in vec3 attrib_position;
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layout(location = 1) in vec2 attrib_texcoord;
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layout(location = 2) in vec3 attrib_normal;
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layout(location = 3) in int attrib_clustercount;
废弃 in/out 用于显式标明该变量的一些布局属性
2.uniform变量
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glsl代码
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#version 330
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uniform sampler2D basetex1;
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uniform float fAlphaRestrictVal;
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uniform mat4 matModel;
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uniform mat4 matView;
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uniform mat4 matProj;
glGetUniformLocation 麻烦
glUseProgram glUseProgram glProgramUniform glUniform glUseProgram glProgramUniform glUseProgram
大量的 上限值 MD5模型的格式、导入与顶点蒙皮式骨骼动画II ] TBO 一维纹理的Buffe
Uniform Buffer Object(UBO)
学一学，VBO
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glsl代码
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#version 330
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layout(std140) uniform matVP
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{
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mat4 matProj;
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mat4 matView;
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};
Interface block
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OpenGL代码
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GLint nMatVPBlockIndex = glGetUniformBlockIndex(nProgramHandler, "matVP");
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//GLint nMatVPBlockIndex = glGetProgramResourceIndex(nProgramHandler, GL_UNIFORM_BLOCK, "matVP");
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if (GL_INVALID_INDEX != nMatVPBlockIndex)
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{
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GLint nBlockDataSize = 0;
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glGetActiveUniformBlockiv(nProgramHandler, nMatVPBlockIndex, GL_UNIFORM_BLOCK_DATA_SIZE, &nBlockDataSize);
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glGenBuffers(1, &m_nUBO);
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glBindBuffer(GL_UNIFORM_BUFFER, m_nUBO);
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glBufferData(GL_UNIFORM_BUFFER, nBlockDataSize, NULL, GL_DYNAMIC_DRAW);
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glBindBufferRange(GL_UNIFORM_BUFFER, 0, m_nUBO, 0, nBlockDataSize);
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glUniformBlockBinding(nProgramHandler, nMatVPBlockIndex, 0);
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glBindBuffer(GL_UNIFORM_BUFFER, NULL);
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}
glGetUniformBlockIndex glGetProgramResourceIndex glGetActiveUniformBlockiv
把它们都关联到同一个uniform buffer binding-point glBindBufferBase glBindBufferRange glUniformBlockBinding
binding-point 这个中间物件保存着能够直达具体某个UBO数据区的“方式”（不妨暂假想为该数据区的起始显存地址、长度等）
36 glBindBufferBase/glBindBufferRange glUniformBlockBinding glUniformBlockBinding
乱弹纪录IV:Transform Feedback ] Transform Feedback Buffer
单个UBO多个uniform-block 每个uniform block对应该UBO存储区域中不同的分区域 glBindBufferRange
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OpenGL代码
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GLint nMatVPBlockIndex = glGetUniformBlockIndex(nProgramHandler, "matVP");
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GLint nCloudScaleIndex = glGetUniformBlockIndex(nProgramHandler, "Scale");
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if (GL_INVALID_INDEX != nMatVPBlockIndex && GL_INVALID_INDEX != nCloudScaleIndex)
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{
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int nUniformBufferAlignSize = 0;
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glGetIntegerv(GL_UNIFORM_BUFFER_OFFSET_ALIGNMENT, &nUniformBufferAlignSize);
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GLint nBlockDataSize1 = 0, nBlockDataSize2 = 0;
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glGetActiveUniformBlockiv(nProgramHandler, nMatVPBlockIndex, GL_UNIFORM_BLOCK_DATA_SIZE, &nBlockDataSize1);
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glGetActiveUniformBlockiv(nProgramHandler, nCloudScaleIndex, GL_UNIFORM_BLOCK_DATA_SIZE, &nBlockDataSize2);
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glGenBuffers(1, &m_nUBO);
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glBindBuffer(GL_UNIFORM_BUFFER, m_nUBO);
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glBufferData(GL_UNIFORM_BUFFER, nUniformBufferAlignSize + nBlockDataSize2, NULL, GL_DYNAMIC_DRAW);
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glBindBufferRange(GL_UNIFORM_BUFFER, 0, m_nUBO, 0, nBlockDataSize1);
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glUniformBlockBinding(nProgramHandler, nMatVPBlockIndex, 0);
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glBindBufferRange(GL_UNIFORM_BUFFER, 1, m_nUBO, nUniformBufferAlignSize, nBlockDataSize2);
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glUniformBlockBinding(nProgramHandler, nCloudScaleIndex, 1);
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}
同一个UBO的两个区域 数据对齐 记住了，block与block的数据不是紧紧pack在一起的
单个uniform-block里面的数据，也有字节对齐的机制
packed、shared、std140
【UBO的一个最显眼的好处就是实现数据共享。譬如我上面的matPV这个uniform block就是最好的例子：通常渲染场景时，只会有一个视图矩阵和一个投影矩阵（[[乱弹OpenGL中的矩阵变换(上)] [乱弹OpenGL中的矩阵变换(下)] ），而且它们相对每一帧都是固定数据。而我们可能场景里物件用到的Shader不一样，但它们都得通过这两个矩阵计算最终的顶点输出啊？以前的话，我得每个Shader都传一次这些相同的矩阵数据，不仅时间上glUniform族函数会比较多而且空间上也分别占每个ShaderProgram本身的同等的存储资源。如今把它们统一在一个UBO中，每帧更新就只要更新UBO一次就可以了，而且也只占一份的资源空间（在显存上）。】
而shared（顺带一提，这个是默认layout）与std140不同之处在于 首选这类std
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glsl代码
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layout(std140) uniform matVP
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{
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float elapsedTime;
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mat4 matProj;
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mat4 matView;
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};
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layout(std140) uniform Scale
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{
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uniform float cloudScale;
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};
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C++代码
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{
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//Render
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glBindBuffer(GL_UNIFORM_BUFFER, m_nUBO);
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glBufferSubData(GL_UNIFORM_BUFFER, 0, sizeof(GLfloat), &fElapsed);
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//current std140 alignment(for base sclaer): 16
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glBufferSubData(GL_UNIFORM_BUFFER, 16, sizeof(Matrix16), m_mtProj.mt);
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glBufferSubData(GL_UNIFORM_BUFFER, 16 + sizeof(Matrix16), sizeof(Matrix16), m_mtView.mt);
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//GL_UNIFORM_BUFFER_OFFSET_ALIGNMENT: 256
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glBufferSubData(GL_UNIFORM_BUFFER, 256, sizeof(GLfloat), &fCScale);
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glBindBuffer(GL_UNIFORM_BUFFER, NULL);
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}
两个重要优 glUniform
glUniform/glProgramUniform
3.varying变量
glShadeModel 需要光栅化时传入参数GL_SMOOTH，不需要时传入GL_FLAT
乱弹纪录I:Geometry Shader glProvokingVertex
flat
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glsl代码
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//vertex shader or geometry shadr
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flat out float visibility;
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//fragment shader
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flat in float visibility;
乱弹纪录I:Geometry Shader ] 一个ShaderProgram中不能有两个同为输入的同名varing变量 也不能有两个同为输出的同名varing变量存在
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glsl代码
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//Vertex Shader
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out vec2 varying_vg_texcoord;
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//Geometry Shader
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in vec2 varying_vg_texcoord[];
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out vec2 varying_gf_texcoord;
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//Fragment Shader
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in vec2 varying_gf_texcoord;
interface block
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//Vertex Shader
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out Varying
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{
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vec2 texcoord;
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}VaryingOut;
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//Geometry Shader
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in Varying
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{
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vec2 texcoord;
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}VaryingIn[];
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out Varying
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{
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vec2 texcoord;
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}VaryingOut;
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//Fragment Shader
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in Varying
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{
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vec2 texcoord;
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}VaryingIn;
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glsl代码
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//Geometry Shader Example
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void main(void)
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{
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for(int i = 0; i < gl_in.length(); ++i)
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{
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gl_Position = gl_in[i].gl_Position;
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VaryingOut.texcoord = VaryingIn[i].texcoord;
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EmitVertex();
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}
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EndPrimitive();
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}
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glsl代码
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//Geometry Shader Example
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out Varying
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{
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vec3 position;
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int cloudcount;
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vec3 dimension;
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}VaryingOut;
乱弹纪录IV:Transform Feedback
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C++代码
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//OpenGL Code Example
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const GLchar *varyingOutCloudFeed[] = {"Varying.position", "Varying.cloudcount", "Varying.dimension"};
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glTransformFeedbackVaryings(m_CloudFeedShader.GetProgramHandler(), 3, varyingOutCloudFeed, GL_SEPARATE_ATTRIBS);
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m_CloudFeedShader.Link();
4.fragmentShader输出
学一学，FBO MRT glBindFragDataLocation
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glsl代码 (fragemnt shader)
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//单输出
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layout(location = 0) out vec4 fragColor;
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//MRT
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layout(location = 0) out vec4 fragColor0;
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layout(location = 1) out vec4 fragColor1;
layout里的关键字其实还有个index
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glsl代码 (fragemnt shader)
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layout(location = 0, index = 0) out vec4 fragColor;
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layout(location = 0, index = 1) out vec4 src1Color;
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C++代码
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glEnable(GL_BLEND);
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glBlendFunc(GL_SRC_ALPHA, GL_SRC1_COLOR);
文章来源: panda1234lee.blog.csdn.net，作者：panda1234lee，版权归原作者所有，如需转载，请联系作者。
原文链接：panda1234lee.blog.csdn.net/article/details/51498303
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