使用 Alpha 渲染纹理问题
当我渲染到纹理，然后绘制相同的图像时，它似乎使一切变得更暗。 要获取此图像：
http://img24.imageshack.us/img24/8061/87993367 .png
我正在将颜色为 (1, 1, 1, .8) 的左上角方块渲染为纹理，然后渲染该纹理，加上中间的方块（相同颜色） ）到另一个纹理，然后最后将该纹理加上右下方块（相同颜色）到屏幕上。
正如你所看到的，每次我渲染到纹理时，一切都会变得有点暗。
我的渲染到纹理代码如下所示：（我在 iPhone 上使用 OpenGL ES）
// gen framebuffer
GLuint framebuffer;
glGenFramebuffersOES(1, &framebuffer);
glBindFramebufferOES(GL_FRAMEBUFFER_OES, framebuffer);
// gen texture
GLuint texture;
glGenTextures(1, &texture);
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, texture);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, 0);
glBindTexture(GL_TEXTURE_2D, 0);
glDisable(GL_TEXTURE_2D);
// hook it up
glFramebufferTexture2DOES(GL_FRAMEBUFFER_OES, GL_COLOR_ATTACHMENT0_OES, GL_TEXTURE_2D, texture, 0);
if(glCheckFramebufferStatusOES(GL_FRAMEBUFFER_OES) != GL_FRAMEBUFFER_COMPLETE_OES))
return false;
// set up drawing
glBindFramebufferOES(GL_FRAMEBUFFER_OES, framebuffer);
glViewport(0, 0, Screen::Width, Screen::Height);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0, Screen::Width, 0, Screen::Height, -1, 1);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glColor4f(1, 1, 1, 1);
// do whatever drawing we'll do here
Draw();
glBindFramebufferOES(GL_FRAMEBUFFER_OES, 0);
我在这里做错了什么吗？ 您需要更多代码来弄清楚吗？ 这里可能发生了什么？
When I render to texture, and then draw the same image, it seems to make everything darker. To get this image:
http://img24.imageshack.us/img24/8061/87993367.png
I'm rendering the upper-left square with color (1, 1, 1, .8) to a texture, then rendering that texture, plus the middle square (same color) to another texture, then finally that texture plus the lower-right square (same color) to the screen.
As you can see, each time I render to texture, everything gets a little darker.
My render-to-texture code looks like: (I'm using OpenGL ES on the iPhone)
// gen framebuffer
GLuint framebuffer;
glGenFramebuffersOES(1, &framebuffer);
glBindFramebufferOES(GL_FRAMEBUFFER_OES, framebuffer);
// gen texture
GLuint texture;
glGenTextures(1, &texture);
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, texture);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, 0);
glBindTexture(GL_TEXTURE_2D, 0);
glDisable(GL_TEXTURE_2D);
// hook it up
glFramebufferTexture2DOES(GL_FRAMEBUFFER_OES, GL_COLOR_ATTACHMENT0_OES, GL_TEXTURE_2D, texture, 0);
if(glCheckFramebufferStatusOES(GL_FRAMEBUFFER_OES) != GL_FRAMEBUFFER_COMPLETE_OES))
return false;
// set up drawing
glBindFramebufferOES(GL_FRAMEBUFFER_OES, framebuffer);
glViewport(0, 0, Screen::Width, Screen::Height);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0, Screen::Width, 0, Screen::Height, -1, 1);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glColor4f(1, 1, 1, 1);
// do whatever drawing we'll do here
Draw();
glBindFramebufferOES(GL_FRAMEBUFFER_OES, 0);
Is there anything that I'm doing wrong here? Do you need more code to figure it out? What might be going on here?
如果你对这篇内容有疑问，欢迎到本站社区发帖提问 参与讨论，获取更多帮助，或者扫码二维码加入 Web 技术交流群。
绑定邮箱获取回复消息
由于您还没有绑定你的真实邮箱，如果其他用户或者作者回复了您的评论，将不能在第一时间通知您！
发布评论
评论（1）
我只是猜测：
绘制第一个纹理在 RGB 和 Alpha 通道中为您提供 204 (0.8 * 255)。 当你第二次绘制时（我认为启用了 GL_BLEND），你会得到带有 80% alpha 的浅灰色 204 RGB，这给你一个中等灰色。
解决方案：使用
glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA)并预乘颜色。I'm only guessing:
Drawing the first texture gives you 204 (0.8 * 255) in the RGB and alpha channels. When you draw for the second time (with GL_BLEND enabled, I presume), you're getting the light gray 204 RGB with 80% alpha which gives you a medium gray.
Solution: use
glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA)and premultiply your colors.