我通过SDL_ttf在OpenGL中显示文本有问题.我编写了LoadFont()函数,它可以加载字体并生成OpenGL纹理.
int LoadFont( char *name, GLubyte r, GLubyte g, GLubyte b, char *text, int ptsize)
{
SDL_Color color = {r, g, b, 0};
TTF_Font *font = TTF_OpenFont(name, ptsize);
Uint32 rmask, gmask, bmask, amask;
#if SDL_BYTEORDER == SDL_BIG_ENDIAN
rmask = 0xff000000;
gmask = 0x00ff0000;
bmask = 0x0000ff00;
amask = 0x000000ff;
#else
rmask = 0x000000ff;
gmask = 0x0000ff00;
bmask = 0x00ff0000;
amask = 0xff000000;
#endif
SDL_Surface *msg = TTF_RenderText_Blended(font, text, color);
SDL_SetAlpha(msg, 0, 0);
if(!msg) {
printf("Unable to Render text\n");
return -1;
}
SDL_Surface *tmp = SDL_CreateRGBSurface(0, msg->w, msg->h, 32, rmask, gmask, bmask, amask);
SDL_BlitSurface(msg, NULL, tmp, NULL);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glGenTextures(1, &texture[0]);
glBindTexture(GL_TEXTURE_2D, texture[0]);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, msg->w, msg->h, 0, GL_RGBA,
GL_UNSIGNED_BYTE, msg->pixels);
return 1;
}
我在initGL()中使用此函数：
int initGL( GLvoid )
{
glViewport(0, 0, SCREEN_WIDHT, SCREEN_HEIGHT);
LoadFont("THWACK.TTF", 255, 255, 255, "Hello!", 14);
glEnable(GL_TEXTURE_2D);
glClearColor(0.0f, 0.0f, 1.0f, 0.0f);
glClearDepth(1.0);
glDepthFunc(GL_LESS);
glEnable(GL_DEPTH_TEST);
glShadeModel(GL_SMOOTH);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(45.0f, (GLfloat)SCREEN_WIDHT/(GLfloat)SCREEN_HEIGHT, 0.1f, 100.0f);
glMatrixMode(GL_MODELVIEW);
return TRUE;
}
此外,我尝试在多边形上显示此文本：
int drawGLScene( GLvoid )
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glLoadIdentity();
glTranslatef(0.0f, 0.0f, -5.0f);
glBindTexture(GL_TEXTURE_2D, texture[0]);
glEnable(GL_TEXTURE_2D);
glBegin(GL_POLYGON);
glTexCoord2f(0.0f, 0.0f); glVertex2f(-1.0f, -1.0f);
glTexCoord2f(1.0f, 0.0f); glVertex2f(1.0f, -1.0f);
glTexCoord2f(1.0f, 1.0f); glVertex2f(1.0f, 1.0f);
glTexCoord2f(0.0f, 1.0f); glVertex2f(-1.0f, 1.0f);
glEnd();
glDisable(GL_TEXTURE_2D);
SDL_GL_SwapBuffers();
return TRUE;
}
但文本不显示,只有白色多边形.
最佳答案 GL_TEXTURE_MIN_FILTER默认为GL_NEAREST_MIPMAP_LINEAR.
如果您请求mipmapping并且不上传完整的mipmap,您将获得白色纹理.
你有这个：
// disable mipmapping on default texture
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
// create new texture, with default filtering state (==mipmapping on)
glGenTextures(1, &texture[0]);
glBindTexture(GL_TEXTURE_2D, texture[0]);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, msg->w, msg->h, 0, GL_RGBA,
GL_UNSIGNED_BYTE, msg->pixels);
请尝试此序列：
// create new texture, with default filtering state (==mipmapping on)
glGenTextures(1, &texture[0]);
glBindTexture(GL_TEXTURE_2D, texture[0]);
// disable mipmapping on the new texture
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, msg->w, msg->h, 0, GL_RGBA,
GL_UNSIGNED_BYTE, msg->pixels);
纹理过滤状态属于纹理对象而不是纹理单元,因此glBindTexture()之后的glTexParameterf()：
OpenGL 2.1 spec,第3.8.11节(第180页)和第3.8.12节(第182页)：
3.8.11: …Next, there are the two sets of texture properties; each consists of the selected minification and magnification filters…
3.8.12: …The resulting texture object is a new state vector, comprising all the state values listed in section 3.8.11, set to the same initial values…
编辑：如果要使用TTF_Render * _Blended(),还必须在渲染之前启用混合：
glEnable( GL_BLEND );
glBlendFunc( GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA );
glColor3ub( 255, 255, 255 );
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, stringTex );
glBegin(GL_QUADS);
...
例：
#include <SDL.h>
#include <SDL_ttf.h>
#include <SDL_opengl.h>
GLuint TextToTexture( TTF_Font* font, GLubyte r, GLubyte g, GLubyte b, const char* text, int ptsize )
{
SDL_Color color = { r, g, b };
SDL_Surface* msg = TTF_RenderText_Blended( font, text, color );
// create new texture, with default filtering state (==mipmapping on)
GLuint tex;
glGenTextures( 1, &tex );
glBindTexture( GL_TEXTURE_2D, tex );
// disable mipmapping on the new texture
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR );
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );
glTexImage2D( GL_TEXTURE_2D, 0, GL_RGBA, msg->w, msg->h, 0, GL_RGBA, GL_UNSIGNED_BYTE, msg->pixels );
SDL_FreeSurface( msg );
return tex;
}
GLuint stringTex = 0;
void drawGLScene( int winWidth, int winHeight )
{
glViewport(0, 0, winWidth, winHeight );
glClearColor(0.0f, 0.0f, 1.0f, 0.0f);
glClearDepth(1.0);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(45.0f, winWidth / (float)winHeight, 0.1f, 100.0f);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(0.0f, 0.0f, -5.0f);
// this is where the magic happens
glEnable( GL_BLEND );
glBlendFunc( GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA );
glColor3ub( 255, 255, 255 );
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, stringTex );
glBegin(GL_QUADS);
glTexCoord2f( 0.0f, 0.0f ); glVertex2f( -1.0f, -1.0f );
glTexCoord2f( 1.0f, 0.0f ); glVertex2f( 1.0f, -1.0f );
glTexCoord2f( 1.0f, 1.0f ); glVertex2f( 1.0f, 1.0f );
glTexCoord2f( 0.0f, 1.0f ); glVertex2f( -1.0f, 1.0f );
glEnd();
glDisable(GL_TEXTURE_2D);
}
int main( int argc, char *argv[] )
{
SDL_Init( SDL_INIT_EVERYTHING );
SDL_Surface* display = SDL_SetVideoMode( 640, 480, 32, SDL_OPENGL );
if( -1 == TTF_Init() )
return -1;
// http://unifoundry.com/unifont.html
TTF_Font *font = TTF_OpenFont( "unifont.ttf", 14 );
stringTex = TextToTexture( font, 255, 255, 255, "Hello!", 14 );
glDepthFunc(GL_LESS);
glEnable(GL_DEPTH_TEST);
glShadeModel(GL_SMOOTH);
bool running = true;
while( running )
{
SDL_Event event;
while( SDL_PollEvent( &event ) )
{
if( event.type == SDL_QUIT )
{
running = false;
break;
}
}
drawGLScene( display->w, display->h );
SDL_GL_SwapBuffers();
SDL_Delay( 16 );
}
TTF_CloseFont(font);
TTF_Quit();
SDL_Quit();
return 0;
}
