glPolygonMode 未以正确模式呈现
glPolygonMode not rendering in correct mode
我最近开始学习镶嵌，今天我试图在镶嵌后画一个三角形，这样我就可以使用 glPolygonMode(GL_FRONT_AND_BACK, GL_LINE) 看到所有镶嵌的小三角形。但由于某种原因，输出只是一个没有任何三角形的彩色背景。
对于镶嵌，我做了一个 control shader 和 evaluation shader 然后 link 它们到 program。（下面的代码）
// Source code for Tesselation Control Shader
static const GLchar * tesselation_control_shader[] =
{
"#version 450 core \n"
" \n"
"layout(vertices = 3) out; \n"
" \n"
"void main(void) \n"
"{ \n"
" //Only if I am invocation 0 \n"
" if (gl_InvocationID == 0) \n"
" { \n"
" gl_TessLevelInner[0] = 5.0; \n"
" gl_TessLevelOuter[0] = 5.0; \n"
" gl_TessLevelOuter[1] = 5.0; \n"
" gl_TessLevelOuter[2] = 5.0; \n"
" } \n"
" \n"
" // Everybody copies their input to their input \n"
" gl_out[gl_InvocationID].gl_Position = \n"
" gl_in[gl_InvocationID].gl_Position; \n"
"} \n"
};
// Source code for tesselation evaluation shader
static const GLchar * tesselation_evaluation_shader[] =
{
"#version 450 core \n"
" \n"
"layout(triangles, equal_spacing, cw) in; \n"
" \n"
"void main(void) \n"
"{ \n"
" gl_Position = (gl_TessCoord.x * gl_in[0].gl_Position + \n"
" gl_TessCoord.y * gl_in[1].gl_Position + \n"
" gl_TessCoord.z * gl_in[2].gl_Position); \n"
"} \n"
};
然后我在 render 函数中调用 glPolygonMode(GL_FRONT_AND_BACK, GL_LINE)，然后使用 glDrawArrays(GL_TRIANGLE, 0, 3) 绘制三角形。
我最初认为 glPolygonMode 默认为 GL_FILL 但我认为这不是问题，因为我只是在看一本书（OpenGL Superbible 第 7 版）。
我该如何解决这个问题？
编辑：
我在下面添加了整个程序的代码：
GLuint compile_shaders(void)
{
GLuint vertex_shader;
GLuint fragment_shader;
GLuint control_shader;
GLuint evaluation_shader;
GLuint program;
// Source code for Vertex Shader
static const GLchar * vertex_shader_source[] =
{
"#version 450 core \n"
" \n"
"// offset and color are input vertex attribute \n"
"layout (location = 0) in vec4 offset; \n"
"layout (location = 1) in vec4 color; \n"
" \n"
"//Declare VS_OUT as an output interface block \n"
"out VS_OUT \n"
"{ \n"
" vec4 color; //Send color to next stage \n"
"}vs_out; \n"
" \n"
"void main(void) \n"
"{ \n"
" //Decalre a hardcoded array of positions \n"
" const vec4 vertices[3] = vec4[3](vec4(0.25, -0.25, 0.5, 1.0), \n"
" vec4(-0.25, -0.25, 0.5, 1.0), \n"
" vec4(0.25, 0.25, 0.5, 1.0)); \n"
" \n"
" //Index into our array using gl_VertexID \n"
" gl_Position = vertices[gl_VertexID] + offset; \n"
" \n"
"//color = vec4(1.0, 0.0, 0.0, 1.0); \n"
"//Output fixed value for vs_color \n"
"vs_out.color = color; \n"
"} \n"
};
// Source code for Fragment Shader
static const GLchar * fragment_shader_source[] =
{
"#version 450 core \n"
" \n"
"//Declare VS_OUT as an input interface block \n"
"in VS_OUT \n"
"{ \n"
" vec4 color; //Send color to next stage \n"
"}fs_in; \n"
" \n"
"//Ouput to the framebuffer \n"
"out vec4 color; \n"
" \n"
"void main(void) \n"
"{ \n"
"// Simply assign the color we were given by the vertex shader to our output \n"
" color = fs_in.color; \n"
"} \n"
};
// Source code for Tesselation Control Shader
static const GLchar * tesselation_control_shader[] =
{
"#version 450 core \n"
" \n"
"layout(vertices = 3) out; \n"
" \n"
"void main(void) \n"
"{ \n"
" //Only if I am invocation 0 \n"
" if (gl_InvocationID == 0) \n"
" { \n"
" gl_TessLevelInner[0] = 5.0; \n"
" gl_TessLevelOuter[0] = 5.0; \n"
" gl_TessLevelOuter[1] = 5.0; \n"
" gl_TessLevelOuter[2] = 5.0; \n"
" } \n"
" \n"
" // Everybody copies their input to their input \n"
" gl_out[gl_InvocationID].gl_Position = \n"
" gl_in[gl_InvocationID].gl_Position; \n"
"} \n"
};
// Source code for tesselation evaluation shader
static const GLchar * tesselation_evaluation_shader[] =
{
"#version 450 core \n"
" \n"
"layout(triangles, equal_spacing, cw) in; \n"
" \n"
"void main(void) \n"
"{ \n"
" gl_Position = (gl_TessCoord.x * gl_in[0].gl_Position + \n"
" gl_TessCoord.y * gl_in[1].gl_Position + \n"
" gl_TessCoord.z * gl_in[2].gl_Position); \n"
"} \n"
};
// Create and compiler Vertex Shader
vertex_shader = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(vertex_shader, 1, vertex_shader_source, NULL);
glCompileShader(vertex_shader);
// Create and compiler Fragment Shader
fragment_shader = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fragment_shader, 1, fragment_shader_source, NULL);
glCompileShader(fragment_shader);
// Create and compile tesselation control shader
control_shader = glCreateShader(GL_TESS_CONTROL_SHADER);
glShaderSource(control_shader, 1, tesselation_control_shader, NULL);
glCompileShader(control_shader);
// Create and compile tesselation evaluation shader
evaluation_shader = glCreateShader(GL_TESS_CONTROL_SHADER);
glShaderSource(evaluation_shader, 1, tesselation_control_shader, NULL);
glCompileShader(evaluation_shader);
// Create program, attach shaders to it, and link it
program = glCreateProgram();
glAttachShader(program, vertex_shader);
glAttachShader(program, fragment_shader);
glAttachShader(program, control_shader);
glAttachShader(program, evaluation_shader);
glLinkProgram(program);
// Delete shaders as program has them now
glDeleteShader(vertex_shader);
glDeleteShader(fragment_shader);
glDeleteShader(control_shader);
glDeleteShader(evaluation_shader);
return program;
};
class TesselationCSOne : public sb7::application
{
public:
void startup()
{
rendering_program = compile_shaders();
glCreateVertexArrays(1, &vertex_array_object);
glBindVertexArray(vertex_array_object);
}
void shutdown()
{
glDeleteVertexArrays(1, &vertex_array_object);
glDeleteProgram(rendering_program);
glDeleteVertexArrays(1, &vertex_array_object);
}
// Our rendering function
void render(double currentTime)
{
// Sets colour
static const GLfloat color[] = { (float)sin(currentTime) * 0.5f + 0.5f, (float)sin(currentTime) * 0.5f + 0.5f, 0.0f, 1.0f };
glClearBufferfv(GL_COLOR, 0, color);
//Tell OpenGL to draw only the outlines of the resulting triangle
glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
// Use program object we created for rendering
glUseProgram(rendering_program);
GLfloat attrib[] = { 1.0, 0.0, 0.0, 0.0 };/*{ (float)sin(currentTime) * 0.5f, (float)sin(currentTime) * 0.6f, 0.0f, 0.0f };*/
// Update value of input attribute 0
glVertexAttrib4fv(0, attrib);
// Draw pathes for tesselation shaders
glPatchParameteri(GL_PATCH_VERTICES, 3);
// Draw one triangle
glDrawArrays(GL_PATCHES, 0, 3);
}
private:
GLuint rendering_program;
GLuint vertex_array_object;
};
// Only instance of DECLARE_MAIN to state entry point
DECLARE_MAIN(TesselationCSOne);
如果您使用曲面细分着色器，则必须绘制补丁。您必须通过 glPatchParameteri( GL_PATCH_VERTICES, ...) 设置补丁的大小，原始类型必须是 GL_PATCHES.
如果一个面片的顶点数是3，那么你必须这样做：
glPatchParameteri(GL_PATCH_VERTICES, 3);
glDrawArrays(GL_PATCHES, 0, 3)
参见OpenGL 4.6 API Core Profile Specification; 10.1.15 Separate Patches; page 342：
Separate patches are specified with mode PATCHES. A patch is an ordered collection of vertices used for primitive tessellation (section 11.2). The vertices comprising a patch have no implied geometric ordering. The vertices of a patch are used by tessellation shaders and the fixed-function tessellator to generate new point, line, or triangle primitives.
void PatchParameteri( enum pname, int value );
with pname set to PATCH_VERTICES
你的着色器程序甚至没有 link，因为片段着色器试图从输入接口块中读取，
未声明为前一个着色器阶段的输出。
您必须通过曲面细分控制和评估着色器将顶点属性传递给片段着色器：
曲面细分控制着色器：
#version 450 core
layout(vertices = 3) out;
in VS_OUT
{
vec4 color;
} tesc_in[];
out TESC_OUT
{
vec4 color;
} tesc_out[];
void main(void)
{
if (gl_InvocationID == 0)
{
gl_TessLevelInner[0] = 5.0;
gl_TessLevelOuter[0] = 5.0;
gl_TessLevelOuter[1] = 5.0;
gl_TessLevelOuter[2] = 5.0;
}
tesc_out[gl_InvocationID].color = tesc_in[gl_InvocationID].color;
gl_out[gl_InvocationID].gl_Position = gl_in[gl_InvocationID].gl_Position;
}
细分评估着色器：
#version 450 core
layout(triangles, equal_spacing, cw) in;
in TESC_OUT
{
vec4 color;
} tese_in[];
out TESE_OUT
{
vec4 color;
} tese_out;
void main(void)
{
tese_out.color = ( gl_TessCoord.x * tese_in[0].color +
gl_TessCoord.y * tese_in[1].color +
gl_TessCoord.z * tese_in[2].color ) / 3.0;
gl_Position = ( gl_TessCoord.x * gl_in[0].gl_Position +
gl_TessCoord.y * gl_in[1].gl_Position +
gl_TessCoord.z * gl_in[2].gl_Position ) / 3.0;
}
片段着色器：
#version 450 core
in TESE_OUT
{
vec4 color;
} fs_in;
out vec4 color;
void main(void)
{
color = fs_in.color;
}
此外，我建议检查着色器对象是否已成功编译：
GLuint shaderObj = .... ;
glCompileShader( shaderObj );
GLint status = GL_TRUE;
glGetShaderiv( shaderObj, GL_COMPILE_STATUS, &status );
if ( status == GL_FALSE )
{
GLint logLen;
glGetShaderiv( shaderObj, GL_INFO_LOG_LENGTH, &logLen );
std::vector< char >log( logLen );
GLsizei written;
glGetShaderInfoLog( shaderObj, logLen, &written, log.data() );
std::cout << "compile error:" << std::endl << log.data() << std::endl;
}
并且着色器程序对象已成功 link编辑：
GLuint progObj = ....;
glLinkProgram( progObj );
GLint status = GL_TRUE;
glGetProgramiv( progObj, GL_LINK_STATUS, &status );
if ( status == GL_FALSE )
{
GLint logLen;
glGetProgramiv( progObj, GL_INFO_LOG_LENGTH, &logLen );
std::vector< char >log( logLen );
GLsizei written;
glGetProgramInfoLog( progObj, logLen, &written, log.data() );
std::cout << "link error:" << std::endl << log.data() << std::endl;
}
顺便读一下Raw string literals，它简化了着色器源代码字符串的声明：
例如
std::string fragment_shader_source = R"(
#version 450 core
in TESE_OUT
{
vec4 color;
} fs_in;
out vec4 color;
void main(void)
{
color = fs_in.color;
}
)";
进一步注意，offset 可能会将三角形移出视口。要么改变属性初始化中offset的值：
GLfloat attrib[] = { 0.0, 0.0, 0.0, 0.0 };
或出于调试原因在顶点着色器中删除 offest
gl_Position = vertices[gl_VertexID];
您必须确保也设置了颜色属性：
GLfloat attrib1[] = { 1.0, 1.0, 0.0, 1.0 };
glVertexAttrib4fv(1, attrib1);
结果可能如下所示：
所以在查看了很多资源和Superbible的代码库后，我意识到我有很多不必要的代码（例如，着色器中的interface blocks）甚至还有很多错误（例如我有两个 program 变量）。
但是，在修复所有生成所需输出（镶嵌三角形）的代码之后：
/**
Program to draw a triangle with tesselation.
**/
#include <sb7.h>
class TesselatedTriangle : public sb7::application
{
void init()
{
static const char title[] = "Tessellated Triangle";
sb7::application::init();
memcpy(info.title, title, sizeof(title));
}
virtual void startup()
{
static const char * vertex_shader_source[] =
{
"#version 450 core \n"
" \n"
"void main(void) \n"
"{ \n"
" const vec4 vertices[] = vec4[](vec4( 0.25, -0.25, 0.5, 1.0), \n"
" vec4(-0.25, -0.25, 0.5, 1.0), \n"
" vec4( 0.25, 0.25, 0.5, 1.0)); \n"
" \n"
" gl_Position = vertices[gl_VertexID]; \n"
"} \n"
};
static const char * tesselation_control_shader_source[] =
{
"#version 450 core \n"
" \n"
"layout (vertices = 3) out; \n"
" \n"
"void main(void) \n"
"{ \n"
" if (gl_InvocationID == 0) \n"
" { \n"
" gl_TessLevelInner[0] = 5.0; \n"
" gl_TessLevelOuter[0] = 5.0; \n"
" gl_TessLevelOuter[1] = 5.0; \n"
" gl_TessLevelOuter[2] = 5.0; \n"
" } \n"
" gl_out[gl_InvocationID].gl_Position = gl_in[gl_InvocationID].gl_Position; \n"
"} \n"
};
static const char * tesselation_evaluation_shader_source[] =
{
"#version 450 core \n"
" \n"
"layout (triangles, equal_spacing, cw) in; \n"
" \n"
"void main(void) \n"
"{ \n"
" gl_Position = (gl_TessCoord.x * gl_in[0].gl_Position) + \n"
" (gl_TessCoord.y * gl_in[1].gl_Position) + \n"
" (gl_TessCoord.z * gl_in[2].gl_Position); \n"
"} \n"
};
static const char * fragment_shader_source[] =
{
"#version 450 core \n"
" \n"
"out vec4 color; \n"
" \n"
"void main(void) \n"
"{ \n"
" color = vec4(0.0, 0.8, 1.0, 1.0); \n"
"} \n"
};
rendering_program = glCreateProgram();
// Compile shaders
GLuint vs = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(vs, 1, vertex_shader_source, NULL);
glCompileShader(vs);
GLuint tcs = glCreateShader(GL_TESS_CONTROL_SHADER);
glShaderSource(tcs, 1, tesselation_control_shader_source, NULL);
glCompileShader(tcs);
GLuint tes = glCreateShader(GL_TESS_EVALUATION_SHADER);
glShaderSource(tes, 1, tesselation_evaluation_shader_source, NULL);
glCompileShader(tes);
GLuint fs = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fs, 1, fragment_shader_source, NULL);
glCompileShader(fs);
// Attach shaders to the program
glAttachShader(rendering_program, vs);
glAttachShader(rendering_program, tcs);
glAttachShader(rendering_program, tes);
glAttachShader(rendering_program, fs);
// Link the program
glLinkProgram(rendering_program);
// Generate vertex arrays
glGenVertexArrays(1, &vertex_array_object);
glBindVertexArray(vertex_array_object);
// Declare the drawing mode for the polygons
glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
}
virtual void render(double currentTime)
{
static const GLfloat green[] = { 0.0f, 0.25f, 0.0f, 1.0f };
glClearBufferfv(GL_COLOR, 0, green);
glUseProgram(rendering_program);
glDrawArrays(GL_PATCHES, 0, 3);
}
virtual void shutdown()
{
glDeleteVertexArrays(1, &vertex_array_object);
glDeleteProgram(rendering_program);
}
private:
GLuint rendering_program;
GLuint vertex_array_object;
};
// One and only instance of DECLARE_MAIN
DECLARE_MAIN(TesselatedTriangle)
希望这对遇到同样问题的其他人有所帮助。
我最近开始学习镶嵌，今天我试图在镶嵌后画一个三角形，这样我就可以使用 glPolygonMode(GL_FRONT_AND_BACK, GL_LINE) 看到所有镶嵌的小三角形。但由于某种原因，输出只是一个没有任何三角形的彩色背景。
对于镶嵌，我做了一个 control shader 和 evaluation shader 然后 link 它们到 program。（下面的代码）
// Source code for Tesselation Control Shader
static const GLchar * tesselation_control_shader[] =
{
"#version 450 core \n"
" \n"
"layout(vertices = 3) out; \n"
" \n"
"void main(void) \n"
"{ \n"
" //Only if I am invocation 0 \n"
" if (gl_InvocationID == 0) \n"
" { \n"
" gl_TessLevelInner[0] = 5.0; \n"
" gl_TessLevelOuter[0] = 5.0; \n"
" gl_TessLevelOuter[1] = 5.0; \n"
" gl_TessLevelOuter[2] = 5.0; \n"
" } \n"
" \n"
" // Everybody copies their input to their input \n"
" gl_out[gl_InvocationID].gl_Position = \n"
" gl_in[gl_InvocationID].gl_Position; \n"
"} \n"
};
// Source code for tesselation evaluation shader
static const GLchar * tesselation_evaluation_shader[] =
{
"#version 450 core \n"
" \n"
"layout(triangles, equal_spacing, cw) in; \n"
" \n"
"void main(void) \n"
"{ \n"
" gl_Position = (gl_TessCoord.x * gl_in[0].gl_Position + \n"
" gl_TessCoord.y * gl_in[1].gl_Position + \n"
" gl_TessCoord.z * gl_in[2].gl_Position); \n"
"} \n"
};
然后我在 render 函数中调用 glPolygonMode(GL_FRONT_AND_BACK, GL_LINE)，然后使用 glDrawArrays(GL_TRIANGLE, 0, 3) 绘制三角形。
我最初认为 glPolygonMode 默认为 GL_FILL 但我认为这不是问题，因为我只是在看一本书（OpenGL Superbible 第 7 版）。
我该如何解决这个问题？
编辑：
我在下面添加了整个程序的代码：
GLuint compile_shaders(void)
{
GLuint vertex_shader;
GLuint fragment_shader;
GLuint control_shader;
GLuint evaluation_shader;
GLuint program;
// Source code for Vertex Shader
static const GLchar * vertex_shader_source[] =
{
"#version 450 core \n"
" \n"
"// offset and color are input vertex attribute \n"
"layout (location = 0) in vec4 offset; \n"
"layout (location = 1) in vec4 color; \n"
" \n"
"//Declare VS_OUT as an output interface block \n"
"out VS_OUT \n"
"{ \n"
" vec4 color; //Send color to next stage \n"
"}vs_out; \n"
" \n"
"void main(void) \n"
"{ \n"
" //Decalre a hardcoded array of positions \n"
" const vec4 vertices[3] = vec4[3](vec4(0.25, -0.25, 0.5, 1.0), \n"
" vec4(-0.25, -0.25, 0.5, 1.0), \n"
" vec4(0.25, 0.25, 0.5, 1.0)); \n"
" \n"
" //Index into our array using gl_VertexID \n"
" gl_Position = vertices[gl_VertexID] + offset; \n"
" \n"
"//color = vec4(1.0, 0.0, 0.0, 1.0); \n"
"//Output fixed value for vs_color \n"
"vs_out.color = color; \n"
"} \n"
};
// Source code for Fragment Shader
static const GLchar * fragment_shader_source[] =
{
"#version 450 core \n"
" \n"
"//Declare VS_OUT as an input interface block \n"
"in VS_OUT \n"
"{ \n"
" vec4 color; //Send color to next stage \n"
"}fs_in; \n"
" \n"
"//Ouput to the framebuffer \n"
"out vec4 color; \n"
" \n"
"void main(void) \n"
"{ \n"
"// Simply assign the color we were given by the vertex shader to our output \n"
" color = fs_in.color; \n"
"} \n"
};
// Source code for Tesselation Control Shader
static const GLchar * tesselation_control_shader[] =
{
"#version 450 core \n"
" \n"
"layout(vertices = 3) out; \n"
" \n"
"void main(void) \n"
"{ \n"
" //Only if I am invocation 0 \n"
" if (gl_InvocationID == 0) \n"
" { \n"
" gl_TessLevelInner[0] = 5.0; \n"
" gl_TessLevelOuter[0] = 5.0; \n"
" gl_TessLevelOuter[1] = 5.0; \n"
" gl_TessLevelOuter[2] = 5.0; \n"
" } \n"
" \n"
" // Everybody copies their input to their input \n"
" gl_out[gl_InvocationID].gl_Position = \n"
" gl_in[gl_InvocationID].gl_Position; \n"
"} \n"
};
// Source code for tesselation evaluation shader
static const GLchar * tesselation_evaluation_shader[] =
{
"#version 450 core \n"
" \n"
"layout(triangles, equal_spacing, cw) in; \n"
" \n"
"void main(void) \n"
"{ \n"
" gl_Position = (gl_TessCoord.x * gl_in[0].gl_Position + \n"
" gl_TessCoord.y * gl_in[1].gl_Position + \n"
" gl_TessCoord.z * gl_in[2].gl_Position); \n"
"} \n"
};
// Create and compiler Vertex Shader
vertex_shader = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(vertex_shader, 1, vertex_shader_source, NULL);
glCompileShader(vertex_shader);
// Create and compiler Fragment Shader
fragment_shader = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fragment_shader, 1, fragment_shader_source, NULL);
glCompileShader(fragment_shader);
// Create and compile tesselation control shader
control_shader = glCreateShader(GL_TESS_CONTROL_SHADER);
glShaderSource(control_shader, 1, tesselation_control_shader, NULL);
glCompileShader(control_shader);
// Create and compile tesselation evaluation shader
evaluation_shader = glCreateShader(GL_TESS_CONTROL_SHADER);
glShaderSource(evaluation_shader, 1, tesselation_control_shader, NULL);
glCompileShader(evaluation_shader);
// Create program, attach shaders to it, and link it
program = glCreateProgram();
glAttachShader(program, vertex_shader);
glAttachShader(program, fragment_shader);
glAttachShader(program, control_shader);
glAttachShader(program, evaluation_shader);
glLinkProgram(program);
// Delete shaders as program has them now
glDeleteShader(vertex_shader);
glDeleteShader(fragment_shader);
glDeleteShader(control_shader);
glDeleteShader(evaluation_shader);
return program;
};
class TesselationCSOne : public sb7::application
{
public:
void startup()
{
rendering_program = compile_shaders();
glCreateVertexArrays(1, &vertex_array_object);
glBindVertexArray(vertex_array_object);
}
void shutdown()
{
glDeleteVertexArrays(1, &vertex_array_object);
glDeleteProgram(rendering_program);
glDeleteVertexArrays(1, &vertex_array_object);
}
// Our rendering function
void render(double currentTime)
{
// Sets colour
static const GLfloat color[] = { (float)sin(currentTime) * 0.5f + 0.5f, (float)sin(currentTime) * 0.5f + 0.5f, 0.0f, 1.0f };
glClearBufferfv(GL_COLOR, 0, color);
//Tell OpenGL to draw only the outlines of the resulting triangle
glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
// Use program object we created for rendering
glUseProgram(rendering_program);
GLfloat attrib[] = { 1.0, 0.0, 0.0, 0.0 };/*{ (float)sin(currentTime) * 0.5f, (float)sin(currentTime) * 0.6f, 0.0f, 0.0f };*/
// Update value of input attribute 0
glVertexAttrib4fv(0, attrib);
// Draw pathes for tesselation shaders
glPatchParameteri(GL_PATCH_VERTICES, 3);
// Draw one triangle
glDrawArrays(GL_PATCHES, 0, 3);
}
private:
GLuint rendering_program;
GLuint vertex_array_object;
};
// Only instance of DECLARE_MAIN to state entry point
DECLARE_MAIN(TesselationCSOne);
如果您使用曲面细分着色器，则必须绘制补丁。您必须通过 glPatchParameteri( GL_PATCH_VERTICES, ...) 设置补丁的大小，原始类型必须是 GL_PATCHES.
如果一个面片的顶点数是3，那么你必须这样做：
glPatchParameteri(GL_PATCH_VERTICES, 3);
glDrawArrays(GL_PATCHES, 0, 3)
参见OpenGL 4.6 API Core Profile Specification; 10.1.15 Separate Patches; page 342：
Separate patches are specified with mode
PATCHES. A patch is an ordered collection of vertices used for primitive tessellation (section 11.2). The vertices comprising a patch have no implied geometric ordering. The vertices of a patch are used by tessellation shaders and the fixed-function tessellator to generate new point, line, or triangle primitives.void PatchParameteri( enum pname, int value );with pname set to
PATCH_VERTICES
你的着色器程序甚至没有 link，因为片段着色器试图从输入接口块中读取，
未声明为前一个着色器阶段的输出。
您必须通过曲面细分控制和评估着色器将顶点属性传递给片段着色器：
曲面细分控制着色器：
#version 450 core
layout(vertices = 3) out;
in VS_OUT
{
vec4 color;
} tesc_in[];
out TESC_OUT
{
vec4 color;
} tesc_out[];
void main(void)
{
if (gl_InvocationID == 0)
{
gl_TessLevelInner[0] = 5.0;
gl_TessLevelOuter[0] = 5.0;
gl_TessLevelOuter[1] = 5.0;
gl_TessLevelOuter[2] = 5.0;
}
tesc_out[gl_InvocationID].color = tesc_in[gl_InvocationID].color;
gl_out[gl_InvocationID].gl_Position = gl_in[gl_InvocationID].gl_Position;
}
细分评估着色器：
#version 450 core
layout(triangles, equal_spacing, cw) in;
in TESC_OUT
{
vec4 color;
} tese_in[];
out TESE_OUT
{
vec4 color;
} tese_out;
void main(void)
{
tese_out.color = ( gl_TessCoord.x * tese_in[0].color +
gl_TessCoord.y * tese_in[1].color +
gl_TessCoord.z * tese_in[2].color ) / 3.0;
gl_Position = ( gl_TessCoord.x * gl_in[0].gl_Position +
gl_TessCoord.y * gl_in[1].gl_Position +
gl_TessCoord.z * gl_in[2].gl_Position ) / 3.0;
}
片段着色器：
#version 450 core
in TESE_OUT
{
vec4 color;
} fs_in;
out vec4 color;
void main(void)
{
color = fs_in.color;
}
此外，我建议检查着色器对象是否已成功编译：
GLuint shaderObj = .... ;
glCompileShader( shaderObj );
GLint status = GL_TRUE;
glGetShaderiv( shaderObj, GL_COMPILE_STATUS, &status );
if ( status == GL_FALSE )
{
GLint logLen;
glGetShaderiv( shaderObj, GL_INFO_LOG_LENGTH, &logLen );
std::vector< char >log( logLen );
GLsizei written;
glGetShaderInfoLog( shaderObj, logLen, &written, log.data() );
std::cout << "compile error:" << std::endl << log.data() << std::endl;
}
并且着色器程序对象已成功 link编辑：
GLuint progObj = ....;
glLinkProgram( progObj );
GLint status = GL_TRUE;
glGetProgramiv( progObj, GL_LINK_STATUS, &status );
if ( status == GL_FALSE )
{
GLint logLen;
glGetProgramiv( progObj, GL_INFO_LOG_LENGTH, &logLen );
std::vector< char >log( logLen );
GLsizei written;
glGetProgramInfoLog( progObj, logLen, &written, log.data() );
std::cout << "link error:" << std::endl << log.data() << std::endl;
}
顺便读一下Raw string literals，它简化了着色器源代码字符串的声明：
例如
std::string fragment_shader_source = R"(
#version 450 core
in TESE_OUT
{
vec4 color;
} fs_in;
out vec4 color;
void main(void)
{
color = fs_in.color;
}
)";
进一步注意，offset 可能会将三角形移出视口。要么改变属性初始化中offset的值：
GLfloat attrib[] = { 0.0, 0.0, 0.0, 0.0 };
或出于调试原因在顶点着色器中删除 offest
gl_Position = vertices[gl_VertexID];
您必须确保也设置了颜色属性：
GLfloat attrib1[] = { 1.0, 1.0, 0.0, 1.0 };
glVertexAttrib4fv(1, attrib1);
结果可能如下所示：
所以在查看了很多资源和Superbible的代码库后，我意识到我有很多不必要的代码（例如，着色器中的interface blocks）甚至还有很多错误（例如我有两个 program 变量）。
但是，在修复所有生成所需输出（镶嵌三角形）的代码之后：
/**
Program to draw a triangle with tesselation.
**/
#include <sb7.h>
class TesselatedTriangle : public sb7::application
{
void init()
{
static const char title[] = "Tessellated Triangle";
sb7::application::init();
memcpy(info.title, title, sizeof(title));
}
virtual void startup()
{
static const char * vertex_shader_source[] =
{
"#version 450 core \n"
" \n"
"void main(void) \n"
"{ \n"
" const vec4 vertices[] = vec4[](vec4( 0.25, -0.25, 0.5, 1.0), \n"
" vec4(-0.25, -0.25, 0.5, 1.0), \n"
" vec4( 0.25, 0.25, 0.5, 1.0)); \n"
" \n"
" gl_Position = vertices[gl_VertexID]; \n"
"} \n"
};
static const char * tesselation_control_shader_source[] =
{
"#version 450 core \n"
" \n"
"layout (vertices = 3) out; \n"
" \n"
"void main(void) \n"
"{ \n"
" if (gl_InvocationID == 0) \n"
" { \n"
" gl_TessLevelInner[0] = 5.0; \n"
" gl_TessLevelOuter[0] = 5.0; \n"
" gl_TessLevelOuter[1] = 5.0; \n"
" gl_TessLevelOuter[2] = 5.0; \n"
" } \n"
" gl_out[gl_InvocationID].gl_Position = gl_in[gl_InvocationID].gl_Position; \n"
"} \n"
};
static const char * tesselation_evaluation_shader_source[] =
{
"#version 450 core \n"
" \n"
"layout (triangles, equal_spacing, cw) in; \n"
" \n"
"void main(void) \n"
"{ \n"
" gl_Position = (gl_TessCoord.x * gl_in[0].gl_Position) + \n"
" (gl_TessCoord.y * gl_in[1].gl_Position) + \n"
" (gl_TessCoord.z * gl_in[2].gl_Position); \n"
"} \n"
};
static const char * fragment_shader_source[] =
{
"#version 450 core \n"
" \n"
"out vec4 color; \n"
" \n"
"void main(void) \n"
"{ \n"
" color = vec4(0.0, 0.8, 1.0, 1.0); \n"
"} \n"
};
rendering_program = glCreateProgram();
// Compile shaders
GLuint vs = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(vs, 1, vertex_shader_source, NULL);
glCompileShader(vs);
GLuint tcs = glCreateShader(GL_TESS_CONTROL_SHADER);
glShaderSource(tcs, 1, tesselation_control_shader_source, NULL);
glCompileShader(tcs);
GLuint tes = glCreateShader(GL_TESS_EVALUATION_SHADER);
glShaderSource(tes, 1, tesselation_evaluation_shader_source, NULL);
glCompileShader(tes);
GLuint fs = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fs, 1, fragment_shader_source, NULL);
glCompileShader(fs);
// Attach shaders to the program
glAttachShader(rendering_program, vs);
glAttachShader(rendering_program, tcs);
glAttachShader(rendering_program, tes);
glAttachShader(rendering_program, fs);
// Link the program
glLinkProgram(rendering_program);
// Generate vertex arrays
glGenVertexArrays(1, &vertex_array_object);
glBindVertexArray(vertex_array_object);
// Declare the drawing mode for the polygons
glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
}
virtual void render(double currentTime)
{
static const GLfloat green[] = { 0.0f, 0.25f, 0.0f, 1.0f };
glClearBufferfv(GL_COLOR, 0, green);
glUseProgram(rendering_program);
glDrawArrays(GL_PATCHES, 0, 3);
}
virtual void shutdown()
{
glDeleteVertexArrays(1, &vertex_array_object);
glDeleteProgram(rendering_program);
}
private:
GLuint rendering_program;
GLuint vertex_array_object;
};
// One and only instance of DECLARE_MAIN
DECLARE_MAIN(TesselatedTriangle)
希望这对遇到同样问题的其他人有所帮助。