我最近开始学习曲面细分，今天尝试在曲面细分之后绘制一个三角形，以便可以使用glPolygonMode(GL_FRONT_AND_BACK, GL_LINE)看到所有曲面细分的较小三角形。但是由于某种原因，输出只是彩色背景，其中没有任何三角形。
对于细分，我制作了一个control shader和evaluation shader，然后将它们链接到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，在使用
glPolygonMode(GL_FRONT_AND_BACK, GL_LINE)绘制三角形之前，我先在render函数中调用glDrawArrays(GL_TRIANGLE, 0, 3)。最初我以为
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 7th Edition)。我怎样才能解决这个问题？
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);
最佳答案
如果使用镶嵌细分着色器，则必须绘制补丁。您必须通过 glPatchParameteri( GL_PATCH_VERTICES, ...) 设置补丁的大小，原始类型必须为GL_PATCHES。
如果补丁中的顶点数为3，则必须这样做:
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:
您的着色器程序甚至没有链接，因为片段着色器试图从输入接口(interface)块读取数据，
未声明为上一个着色器阶段的输出。
您必须通过镶嵌控制和评估着色器将顶点属性传递给片段着色器:
镶嵌控制着色器:
#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;
}
镶嵌评估着色器:
#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链接:
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;
}
顺便说一下，阅读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(viewport)。在属性初始化中更改offset的值:GLfloat attrib[] = { 0.0, 0.0, 0.0, 0.0 };
或出于调试原因而放弃了顶点着色器中的
offestgl_Position = vertices[gl_VertexID];
您还必须确保同时设置了color属性:
GLfloat attrib1[] = { 1.0, 1.0, 0.0, 1.0 };
glVertexAttrib4fv(1, attrib1);
结果可能如下所示: