我真的有噩梦来实现我在OpenGles 2.0中所需要的 在发布代码参考之前，让我告诉我需要什么。
我有2D纹理片段着色器。在纹理的顶部，我想绘制红色线。我可以绘制线但是着色为红色不起作用。
着色器声明：
static const char s_v_shader[] =
"attribute vec4 vPosition; \n"
"attribute vec2 my_Texcoor; \n"
"uniform mat4 u_TransMatrix; \n"
"varying vec2 vTexcoor; \n"
"void main() \n"
"{ \n"
" vTexcoor = my_Texcoor; \n"
" gl_Position = u_TransMatrix*vPosition; \n"
"} \n";
static const char s_f_shader[] =
"precision mediump float;\n"
"uniform sampler2D my_Sampler; \n"
"varying vec2 vTexcoor; \n"
"void main() \n"
"{ \n"
" vec4 tex = texture2D(my_Sampler, vTexcoor); \n"
" gl_FragColor = tex; \n"
"} \n";
在纹理之上，我在无限循环中渲染来自相机的视频帧。 在渲染视频之前，我正在使用下面的代码设置2D纹理的坐标。
现在我将从main函数
解释我的代码main()
{
const GLfloat vertices[][2] = {
{ -1.0f, -1.0f},
{ 1.0f, -1.0f},
{ -1.0f, 1.0f},
{ 1.0f, 1.0f}
};
const GLfloat texcoords[][2] = {
{ 0.0f, 1.0f},
{ 1.0f, 1.0f},
{ 0.0f, 0.0f},
{ 1.0f, 0.0f}
};
GLfloat transformMatrix[16] =
{
1.0f, 0.0f, 0.0f, 0.0f,
0.0f, 1.0f, 0.0f, 0.0f,
0.0f, 0.0f, 1.0f, 0.0f,
0.0f, 0.0f, 0.0f, 1.0f
};
// setup OpenGl environment......
Setup_coordinates()
}
Setup_coordinates()
{
LoadShaders(s_v_shader, s_f_shader);
-- Complete function defined below
// By now I should be using shader program.
// Grab location of shader attributes.
GLint locVertices = glGetAttribLocation(programHandle, "vPosition");
GLint locTexcoord = glGetAttribLocation(programHandle, "my_Texcoor");
// Transform Matrix is uniform for all vertices here.
GLint locTransformMat = glGetUniformLocation(programHandle, "u_TransMatrix");
GLint locSampler = glGetUniformLocation(programHandle, "my_Sampler");
/* Create the texture. */
glGenTextures(1, &gTexObj);
glBindTexture(GL_TEXTURE_2D, gTexObj);
if (gTexObj == 0)
{
printf("Could not load the texture \n");
return -1;
}
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glUniformMatrix4fv(locTransformMat, 1, GL_FALSE, transformMatrix);
glUniform1i(locSampler, 0);
glClearColor(0.0f, 0.5f, 0.0f, 0.0f);
glClear(GL_COLOR_BUFFER_BIT);
while(1) -- Infinite loop to render video frames on 2D texture and draw red color line.
{
// enable vertex arrays to push the data.
glEnableVertexAttribArray(locVertices);
glEnableVertexAttribArray(locTexcoord);
// set data in the arrays.
glVertexAttribPointer(locVertices, 2, GL_FLOAT, GL_FALSE, 0, &vertices[0][0]);
glVertexAttribPointer(locTexcoord, 2, GL_FLOAT, GL_FALSE, 0, &texcoords[0][0]);
Render video frames logic goes here...................................
Each frame of video is abosultely rendering fine.
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
Now comes the tricky part to draw the line and color it with red.
float red_left_1[] =
{
-0.85f, -0.9f, -0.6f, -0.5f,
};
glVertexAttribPointer ( 1, 2, GL_FLOAT, GL_FALSE, 0, red_left_1 );
glEnableVertexAttribArray (1 );
glDrawArrays ( GL_LINES , 0, 2 );
glLineWidth( width_test );
}
}
void LoadShaders(const char * vShader, const char * pShader)
{
vertShaderNum = glCreateShader(GL_VERTEX_SHADER);
pixelShaderNum = glCreateShader(GL_FRAGMENT_SHADER);
if (CompileShader(vShader, vertShaderNum) == 0)
{
printf("%d: PS compile failed.\n", __LINE__);
return;
}
if (CompileShader(pShader, pixelShaderNum) == 0)
{
printf("%d: VS compile failed.\n", __LINE__);
return;
}
programHandle = glCreateProgram();
glAttachShader(programHandle, vertShaderNum);
glAttachShader(programHandle, pixelShaderNum);
// Bind vPosition to attribute 0
glBindAttribLocation ( programHandle, 0, "vPosition" );
glLinkProgram(programHandle);
// Check if linking succeeded.
GLint linked = 0;
glGetProgramiv(programHandle, GL_LINK_STATUS, &linked);
if (!linked)
{
printf("%d: Link failed.\n", __LINE__);
// Retrieve error buffer size.
GLint errorBufSize, errorLength;
glGetShaderiv(programHandle, GL_INFO_LOG_LENGTH, &errorBufSize);
char * infoLog = (char*)malloc(errorBufSize * sizeof (char) + 1);
if (infoLog)
{
// Retrieve error.
glGetProgramInfoLog(programHandle, errorBufSize, &errorLength, infoLog);
infoLog[errorBufSize + 1] = '\0';
fprintf(stderr, "%s", infoLog);
free(infoLog);
}
return;
}
glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
glUseProgram(programHandle);
}
大多数天才人士建议如上所述再声明一个着色器，但用统一的vec4颜色替换统一的sampler2D my_Sampler。
void main()
{
gl_FragColor = color
}
然后在使用glUseProgram显示纹理和绘制颜色线的同时在这些着色器程序之间切换。
我试过并且绝对放弃了，因为切换到着色器程序的绘图线不起作用。
答案 0 :(得分：0)
以下是用于生成可用于线条的彩色1x1纹理的代码（位于main或Setup_coordinates）。使用此解决方案，您将不需要另一个着色器。
GLuint lineTexture;
glGenTextures(1, &lineTexture);
unsigned char red[4] = { 255, 0, 0, 255};
glBindTexture(GL_TEXTURE_2D, lineTexture);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 1, 1, 0, GL_RGBA, GL_UNSIGNED_BYTE, red);
glBindTexture(GL_TEXTURE_2D, 0);
在致电glDrawArrays之前，请使用此选项切换到正确的纹理。
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, <lineTexture or gTexObj>);
glUniform1i(locSampler, 0);
一个更通用的解决方案（我个人在我的OpenGL项目中实现）是创建一个白色纹理，为着色器添加一个颜色均匀，并将该系列与texture2D返回值相乘。使用此方法，您可以使用相同的白色纹理创建不同的彩色线条和图形，仅更改颜色均匀。对于视频帧，您将发送白色并且像素将保持不变。这将只需要很少的代码更改，我相信如果你认为它听起来更好，你可以弄明白。 ：）