Question

当我使用GL_HALF_FLOAT_OES纹理时;片段着色器似乎写得很好，我可以观察到它在xCode中使用gpuTrace时具有正确的值。但是当我用

回读它时

glReadPixels( 0, 0, self.imageSize->v[0], self.imageSize->v[1], GL_RGBA, type, pixels );

像素组件浮动-0或浮动1.是否因为浮动值被意外剪切？有没有办法回读最初编写的浮点值？如果我使用GL_RGBA16F_EXT或GL_RGBA32F_EXT代替GL_RGBA，我会收到无效的枚举。

根据Rabbid76的反馈

int formatExt, typeExt;
glGetIntegerv( GL_IMPLEMENTATION_COLOR_READ_FORMAT, &formatExt );
glGetIntegerv( GL_IMPLEMENTATION_COLOR_READ_TYPE, &typeExt );

[ self traceLog:[ NSString stringWithFormat:@"Implementation format is %@, type is %@", [ TextureImage strForFormat:formatExt ], [ TextureImage strForType:typeExt ] ] ];

返回的值是“实现格式为GL_RGBA，类型为GL_HALF_FLOAT_OES”。这可能意味着HALF_FLOAT是它能够回读的唯一值。我仍在调查它是否有可能回读GL_FLOAT，因为尽管glGetIntegerv返回glReadPixels没有用无效的枚举标记GL_FLOAT;它接受并处理它，但漂浮物似乎不是正确的漂浮物;所以它似乎做了一些意想不到的转换。

Answer 1

See the documentation of glReadPixels (OpenGL ES 3.1) which says:

void glReadPixels( GLint x, GLint y, GLsizei width, GLsizei height, GLenum format, GLenum type, GLvoid * data);

format
Specifies the format of the pixel data. The following symbolic values are accepted: GL_RGBA, and GL_RGBA_INTEGER. An implementation-chosen format will also be accepted. This can be queried with glGet and GL_IMPLEMENTATION_COLOR_READ_FORMAT.

type
Specifies the data type of the pixel data. Must be one of GL_UNSIGNED_BYTE, GL_UNSIGNED_INT, GL_UNSIGNED_INT_2_10_10_10_REV, GL_INT, or GL_FLOAT. An implementation-chosen type will also be accepted. This can be queried with glGet and GL_IMPLEMENTATION_COLOR_READ_TYPE.

This means you have to read the implementation-chosen format and type, to read back the float values as they were originally written:

int format = glGet(GL_IMPLEMENTATION_COLOR_READ_FORMAT);
int type   = glGet(GL_IMPLEMENTATION_COLOR_READ_TYPE);
glReadPixels( 
    0, 0, self.imageSize->v[0], self.imageSize->v[1],
    format, type, pixels );

See the documentation of glGet (OpenGL ES 3.1):

GL_IMPLEMENTATION_COLOR_READ_FORMAT params returns one value, the format chosen by the implementation in which pixels may be read from the color buffer of the currently bound framebuffer.

GL_IMPLEMENTATION_COLOR_READ_TYPE params returns one value, the type chosen by the implementation with which pixels may be read from the color buffer of the currently bound framebuffer.

GL_HALF_FLOAT_OES和glReadPixels

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