OpenGL ES；渲染从 CGBitmapContext 创建的纹理 [英] OpenGL ES; rendering texture created from CGBitmapContext

问题描述

我正在执行以下内容，这些内容来自几个不同的教程(只是一个渲染过程，未显示初始化代码，但适用于无纹理的基元):

I am executing the following, which I have derived from a few different tutorials (Just a single render pass, initialisation code not shown but works fine for untextured primitives):

glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrthof(0, xSize, 0, ySize, -1.0f, 1.0f);
glMatrixMode(GL_MODELVIEW);

glColor4f(1.0f, 1.0f, 1.0f, 1.0f);
glEnable(GL_TEXTURE_2D);
glBlendFunc(GL_ONE, GL_SRC_COLOR);

GLuint texture[1];
glGenTextures(1, &texture[0]);
glBindTexture(GL_TEXTURE_2D, texture[0]);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);

int width = 50;
int height = 50;
void* textureData = malloc(width * height * 4);
CGColorSpaceRef cSp = CGColorSpaceCreateDeviceRGB();
CGContextRef ct = CGBitmapContextCreate(textureData, width, height, 8, width*4, cSp, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);

CGContextSetRGBFillColor(ct, 0, 1, 0, 1);
CGContextFillRect(ct, CGRectMake(0, 0, 50, 50));
CGContextRelease(ct);

glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, textureData);

float verts[] = {
0.0f, 0.0f, 0.0f,
50.0f, 0.0f, 0.0f,
0.0f, 50.0f, 0.0f,
50.0f, 50.0f, 0.0f
};

float texCords[] = {
0.0f, 0.0f,
1.0f, 0.0f,
0.0f, 1.0f,
1.0f, 1.0f
};

 glVertexPointer(3, GL_FLOAT, 0, verts);
 glTexCoordPointer(2, GL_FLOAT, 0, texCords);
 glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);

 glDisable(GL_TEXTURE_2D);

结果是一个白色方块.不是预期的绿色.任何人都可以在我的代码中发现导致其无法呈现的错误吗?

The result is a white square. Not the green one as intended. Can anyone spot the error(s) in my code which result in its' failure to render?

我希望让它工作，然后将其移至文本渲染.

I hope to get this working then move it on to text rendering.

推荐答案

问题是 width 和 height 不是二的幂.有两种解决方案:

The problem is that width and height are not powers of two. There are two solutions:

• 使用纹理矩形扩展.将纹理目标设置为 GL_TEXTURE_RECTANGLE_ARB 而不是 GL_TEXTURE_2D.在使用它之前，您必须启用此扩展程序.请注意，矩形纹理不支持 mipmap.
• 对纹理尺寸使用 2 的幂.

• Use the texture rectangle extension. Set the texture target to GL_TEXTURE_RECTANGLE_ARB instead of GL_TEXTURE_2D. You will have to enable this extension before using it. Note that rectangle textures do not support mipmaps.
• Use powers of two for texture dimensions.

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